JMP Validate fixes and Integer Update

Changed how JMPEntries are validated.
Added some missing docstrings.
Created some internal search functions and used them to find jmp fields.
Introduced a few new errors for when fields don't exist to be more explicit than the generic python error.
Fixed an issue where padding was not being calculated correctly.
Removed an un-necessary bytes read.
Fixed an issue where Integer values for JMP files were not updating correctly.