Export segments as html

Export all task segments as html with track changes included. The idea is to generate html file with table where all task segments are listed (similar to changed segments email) and make this exportable via UI and API.

This export type make sense to be implemented as core t5 feature.

Technical concept

Back-end

• New task export type(make sense to have this feature as general translate5 feature) where html will be generated with all segments listed. The export provides the user html files where all segments (including track changes) will be listed in a table (ensure, this also works without trackchanges plug-in and in this case no trackchanges are in the exported html).
• New frontend/backend ACL for this export type
• The export action is to big and it contains to much information. Refactor this so the code is more clean and readable

Front-end

• New menu option in the task action export menu: Segment changes
• Visible and available all type of pm users (everyone who is able to export xliff 2.1 should be also able to export the changes)