Cleanup srdft keywords

Cleaned up the srfunctional keywords in srdft().

_S to denote spin-density does not exist anymore, DFT_SPINDNS = .TRUE. is now default inside the program. Added a third keyword to turn of DFT_SPINDNS in case some calculations do not work with it, if SRPBEGWS is wanted without DFT_SPINDNS it can be specified as SRXPBEGWS SRCPBEGWS NO_SPINDENSITY. This is also documented in the manual.

Now the reason to do the above is that before, openshell calculations would give incorrect results if the functional was specified as SRXPBEGWS SRCPBEGWS instead of SRXPBEGWSS SRCPBEGWSS. There would be no indication in the output file either that the result would be incorrect.

Added keyword for LRCLDA and LRCPBEGWS, such that HFSRDFT can be used to run long-range corrected DFT, i.e. only range-separation in the exchange functional.