Bugfix: Plugin controls do not appear on Edit Entry page in MT Pro (MT4 and MT5)

Changed check of product name to regex because MT->product_name can have one of at least 6 possible values in MT4-MT5:

- Movable Type
- Movable Type Open Source
- Movable Type Publishing Platform
- Movable Type Pro
- Movable Type Enterprise
- Movable Type Advanced