Add support for CodeMirror's sqlhint

[arikfr]

Apparently CodeMirror has SQLHint plugin (http://codemirror.net/doc/manual.html#addon_sql-hint):

A simple SQL hinter. Defines CodeMirror.hint.sql. Takes two optional options, tables, a object with table names as keys and array of respective column names as values, and defaultTable, a string corresponding to a table name in tables for autocompletion.

It will be really cool to add support for this.

• Update CodeMirror version
• Add API endpoint that will return database schema per data source.
• Wire this API with SQL hint.
• ...
• Profit!