Uploading locale files it really slow let's make it quicker

Problem/Motivation

Importing translations from PO files is really slow. Drupal core provides PoReaders and PoWriters for files and databases. This process one row at a time which means we make 1000s of database queries. This issue is going to investigate providing an optimised PO loader from file to database in this module and then once we have it tested and working great we can extract it and move it to core.

Proposed resolution

TBD but likely to involve bulk inserting many rows at once.

Remaining tasks

All of them.

User interface changes

None

API changes

TBD

Data model changes

Should be none. Might make use of temporary tables but no data model should change.