Replace Pledgie and Flattr with Gittip [ci skip]
Remove (redundant) 'else nil'.
Clarify code paths and reduce repetition.
Introduce datetime_filter to DRY code.

Also clarified a few statements.
Moved association implementation details to its own class.
Extracted adapter statement building to class.
Made precompile asset list easier to read.
Reduce repetition and fix a couple of typos.
Reduced complexity of individual methods & split up responsibilities.
Allow Pry under test environment.
DRY up active_record adapter methods with WhereBuilder class.
Remove superfluous 'private' declaration.