moved list of enum literals from ViewManager to Columns (which makes them available to the rest of model now)
allow specifying enums as text in filters
in filters allow specifiying boolean columns as strings
removed two unused files
allow specifying record modification status column enum via strings
more cleanup
some UniversalId fixes
allow the use of record types in string filters
allow the use of value types in string filters
rewrote value node to support half-sided intervals (meaning infinity or -infinity for the missing half)
added support for half-sided intervals to filter parser
allow the use of keywords for strings without quotation marks
Merge branch 'filter'