Introduce categories in translate5

Categories should be used to finer granulate tasks, users (and/or customers) in Translate5.

Definition of categories

Currently the available list of categories is defined in the configuration (Zf_configuration) facility. Stored with name/id and label. The label should go the application internal translation process.
For reference: similar configuration exists with segment status and segment QM flags.

In the future it may make sense if categories can be added on the fly when using the below defined tag fields (like in the component dropdown here in JIRA).

For the upcoming multi-tenancy feature the administration of categories should optionally belong to customers - this can be reached through the upcoming overwriting of system config by customer. That means only the for the currently chosen customer available categories are available in the GUI.

Tasks

• When creating / editing a task, add a tag field in the form to add / change the categories.
• In the task grid the categories are listed as separate grid column, in a filterable way
• vi API the categories should be easily addable / changeable, for example a "categories" field containing just an array of the categories.

Users

• When creating / editing a task, add a tag field in the form to add / change the categories.
• In the task grid the categories are listed as separate grid column, in a filterable way
• vi API the categories should be easily addable / changeable, for example a "categories" field containing just an array of the categories.

Automatically user to task adding

Currently users (editors and if enabled PMs too) are added automatically to a new task if the language combination of the user matches to the task. This matching should be extended by additional category matching. So add users only if languages and categories match.

A summary about all automatically uses should be send to the PM of the task. The subject should contain already the number of added users, so that the PM can find out easily tasks where no user was added.