SQL-like filter queries

[mafrosis]

Replace the IssueFilter as it stands with a new SQL-like interface based on moz-sql-parser

The --filter param will only accept the WHERE clause, but with a basic select 1 from blah prefix, we can extract a structured query.

>>> from moz_sql_parser import parse
>>> parse('select 1 from blah where assignee = mafro')
{'select': {'value': 1}, 'from': 'blah', 'where': {'eq': ['assignee', 'mafro']}}
>>> parse('select 1 from blah where assignee = mafro and fixversion = PI12')
{'select': {'value': 1}, 'from': 'blah', 'where': {'and': [{'eq': ['assignee', 'mafro']}, {'eq': ['fixversion', 'PI12']}]}}

Pair this with pandas query() method to execute dynamic filters on the underlying DataFrame.

Expose on the CLI via a --filter param, and drop the --projects filter.

[mafrosis]

Closed in #98