Make from_file and other laser init compatible

[huixingjian]

This PR intends to fix the confliction that no user-defined laser could be generated when reading laser from file.

Combining with PR #1122 and PR #866, the code can now initialise multiple lasers by parser\gaussian\from_file.

-The default option of <laser name>. init_type would be gaussian. And another two options are parser from_file.

Note that the central wavelength of all the lasers ought to be identical on current setting. An error will be raised if the value of lasers.lambda0 doesn't equal to the wavelength loaded from file.

[huixingjian]

With the input of

lasers.names = gaussian parser ff 
lasers.lambda0 = 800e-9
lasers.solver_type = multigrid
lasers.MG_tolerance_rel = 1e-5
gaussian.a0 = 1.9
gaussian.position_mean = 0. 15e-6 0
gaussian.w0 = 20e-6
gaussian.L0 = 10e-6
parser.init_type =  parser
gaussian.init_type = gaussian
ff.init_type = from_file
parser.laser_real(x,y,z)="2*exp(-(x^2+y^2)/W0^2-z^2/(2*clight^2*tau^2))*cos(-(6.28*z/800e-9))*
                          if(abs(z)<5e-7 and y >0,
                               if(y<(2.25*sqrt(abs(-(abs(z*1e6)-0.5)*(abs(z*1e6)+0.5))/(-(abs(z*1e6)-0.5)*(abs(z*1e6)+0.5))))/1e6,0,1),1)*
                          if(abs(z)>5e-7 and abs(z)<7.5e-7 and y >0,
                               if(y<(3*abs(z*1e6)+0.75*sqrt(abs(-(abs(z*1e6)-0.5)*(abs(z*1e6)-0.75))/(-(abs(1e6*z)-0.5)*(abs(z*1e6)-0.75))))/1e6,0,1),1)*
                          if(abs(z)>7.5e-7 and abs(z)< 1e-6 and y >0,
                               if(y<(9*sqrt(abs(-(abs(z*1e6)-1)*(abs(z*1e6)-0.75))/(-(abs(1e6*z)-1)*(abs(z*1e6)-0.75)))-8*abs(z*1e6))/1e6,0,1),1)*
                          if(abs(z)>1e-6 and abs(z)< 3e-6 and y >0,
                               if(y<(6*sqrt(10)/7+(1.5-0.5*abs(z*1e6))*sqrt(abs(abs(z*1e6)-1)/(abs(z*1e6)-1))-6*sqrt(10)*sqrt(4-(abs(1e6*z)-1)**2)/14)/1e6,0,1),1)*
                          if(abs(z)>3e-6 and abs(z) < 7e-6 and y>0,
                               if(y <(3*sqrt(1-(z*1e6/7)**2)*sqrt(abs(abs(z*1e6)-3)/(abs(z*1e6)-3)))/1e6,0,1),1)*
                          if(abs(z)>4e-6 and abs(z)<7e-6 and y<0,
                               if(y >(-3*sqrt(1-(z*1e6/7)**2)*sqrt(abs(abs(z*1e6)-4)/(abs(z*1e6)-4)))/1e6,0,1),1)*
                          if(abs(z)< 4e-6 and y <0,
                                if(y > (abs(z*1e6/2)-(3*sqrt(33)-7)*(z*1e6)**2/122-3.1+sqrt(1-(abs(abs(z*1e6)-2)-1)**2))/1e6,0,1),1)"
parser.laser_imag(x,y,z)="2*exp(-(x^2+y^2)/W0^2-z^2/(2*clight^2*tau^2))*sin(-(6.28*z/800e-9))*
                          if(abs(z)<5e-7 and y >0,
                               if(y<(2.25*sqrt(abs(-(abs(z*1e6)-0.5)*(abs(z*1e6)+0.5))/(-(abs(z*1e6)-0.5)*(abs(z*1e6)+0.5))))/1e6,0,1),1)*
                          if(abs(z)>5e-7 and abs(z)<7.5e-7 and y >0,
                               if(y<(3*abs(z*1e6)+0.75*sqrt(abs(-(abs(z*1e6)-0.5)*(abs(z*1e6)-0.75))/(-(abs(1e6*z)-0.5)*(abs(z*1e6)-0.75))))/1e6,0,1),1)*
                          if(abs(z)>7.5e-7 and abs(z)< 1e-6 and y >0,
                               if(y<(9*sqrt(abs(-(abs(z*1e6)-1)*(abs(z*1e6)-0.75))/(-(abs(1e6*z)-1)*(abs(z*1e6)-0.75)))-8*abs(z*1e6))/1e6,0,1),1)*
                          if(abs(z)>1e-6 and abs(z)< 3e-6 and y >0,
                               if(y<(6*sqrt(10)/7+(1.5-0.5*abs(z*1e6))*sqrt(abs(abs(z*1e6)-1)/(abs(z*1e6)-1))-6*sqrt(10)*sqrt(4-(abs(1e6*z)-1)**2)/14)/1e6,0,1),1)*
                          if(abs(z)>3e-6 and abs(z) < 7e-6 and y>0,
                               if(y <(3*sqrt(1-(z*1e6/7)**2)*sqrt(abs(abs(z*1e6)-3)/(abs(z*1e6)-3)))/1e6,0,1),1)*
                          if(abs(z)>4e-6 and abs(z)<7e-6 and y<0,
                               if(y >(-3*sqrt(1-(z*1e6/7)**2)*sqrt(abs(abs(z*1e6)-4)/(abs(z*1e6)-4)))/1e6,0,1),1)*
                          if(abs(z)< 4e-6 and y <0,
                                if(y > (abs(z*1e6/2)-(3*sqrt(33)-7)*(z*1e6)**2/122-3.1+sqrt(1-(abs(abs(z*1e6)-2)-1)**2))/1e6,0,1),1)"

ff.input_file=/p/scratch/plasmadiy/janhui/read_file_test/from_file/diags/hdf5/openpmd_000000.h5
ff.iteration = 0

three lasers could be generated