[5.8] Add insert ignore support

[dunhamjared]

Per @taylorotwell, removed SQL Server support.

This pull request adds insert or ignore support to the query builder for the following database engines:

MySQL - uses: insert ignore
Postgres - uses: on conflict do nothing
SQLite - uses: insert or ignore
SqlServer - not supported, throws RuntimeException

Example:

DB::table('test')->insertOrIgnore([['id'=>1], ['id'=>2]]);

Related issue: #9612
Original pull: #29572
Fixes: laravel/ideas#1762