ENH+BF+TST: Filter now returns reference to failregex and ignoreregex

This avoids duplication of code across fail2ban-regex and samples test
cases. This also now more neatly resolves the issue of double counting
date templates matches in fail2ban-regex.
In addition, the samples test cases now also print a warning message
that not all regexs have samples for them, with future plan to change
this to an assertion.
DOC: Comment to fail2ban-regex - flagging lines matched multiple regexs
DOC: Update doc in reference to changes for sample testcases
Merge branch 'filter-failregex-return'

Conflicts:
	server/filter.py