Update user tagging routines to take vector of values

[donnaaboise]

This PR will pass in a full vector (1:meqn) of values at point (i,j) to tagging routines. Input arguments are :

qval(1:meqn)
quad(-1:1,-1:1,1:meqn)
qmin(1:min), qmax(1:meqn)

In addition, there is a new option clawpatch:threshold-variable to allow the user to specify which variable in 1:meqn is used when specified value, difference, gradient etc as refinement options.

This PR will be most useful for computing, for example, pressure, which depends on all state variables.