Implement expression grammar for filters

[jaa127]

For background information, please see #78 and especially #78 (comment).

For example, there should be AND, OR and maybe also NOT. For backwards compatibility, expression filter should start with parenthesis (or some other way it should be possible to support plain filter syntax with implied AND).

For example:
((begin=2016-01-01 AND end=2016-03-01) OR account = .*:Bank:.*)