Set GMX_OCL_FILE_PATH during cmake project configuration

[ancahamuraru]

Set GMX_OCL_FILE_PATH automatically during project configuration.

GMX_OCL_FILE_PATH points to Gromacs src folder. This information should be known during cmake project configuration.

[ancahamuraru]

Setting GMX_OCL_FILE_PATH during project configuration is not a good solution because:

• on Linux, such variables are not system wide persistent
• GMX_OCL_FILE_PATH should be defined only when running the built from source version and not when running the installed version.

Another approach:

if defined (GMX_OCL_FILE_PATH)
    load_ocl_source_files_from(GMX_OCL_FILE_PATH)
else
{   
    detect at runtime if the current app was build from sources relying on a known folder structure
    if (app built from sources)
       load_ocl_source_files_from(known folder structure)
    else
       load_ocl_source_files_from(OCL_INSTALL_FULL_PATH)      
 }

Consider also the option of having the OpenCL device code embedded as strings in the application.

[ancahamuraru]

The way OpenCL source files are loaded has been reimplemented. All changes are included starting with this commit: 93c8d54b6455253d657472d4a05d89e5ae1dc510

• The list of OpenCL kernel files and dependencies does not include any more ishift.h and nbnxn_consts.h.
• OCL_INSTALL_DIR variable which is used for installing OpenCL files stores a relative path
• vectype_ops.clh has been moved to mdlib/nbnxn_ocl (see also the comments below)
• All OpenCL kernel files are expected to be stored in one single folder for both the installed version and the version built from sources.
• defaultJITDataPath method is now used for returning the full path to the folder storing OpenCL kernel files
• GMX_OCL_FILE_PATH has been kept, but has a different purpose: the user can define it only if he/she wants to provide a custom OpenCL source path. It can also be used as a backup if our internal engine fails to identify the OpenCL kernel location.