Factor out the FP_LIB_TABLE specific content from FP_TBL_MODEL into a new
LIB_TABLE_GRID class that can be used for any library table grid mix in.
Create new FP_LIB_TABLE_GRID object for the footprint library edit dialog.
Add method GetEnvVariables() to return any environment variables found in
a LIB_TABLE object.
Rename FPID to LIB_ID as is now used as a generic library identifier and
is no longer specific to footprints.
Remove all mention of footprint from the new LIB_ID doxygen comments and
code.
Rename files fpid.h and fpid.cpp to lib_id.h and lib_id.cpp.
Rename fp_lib_table.keywords file to lib_table.keywords and adjust CMake
build dependencies accordingly.
Update all source files effected by the code and file name changes.
Update .gitignore for file name changes.