Add submissions filter by category

[NateWr]

Describe the problem you would like to solve
Preprint servers and journals that use categories would like to be able to filter the submission lists by assigned category.

Describe the solution you'd like
Add a filter to the submissions list that allows the submissions list to be filtered by categories. This can use the same format as the sections filter: when there are fewer than 5 categories, show filters as a list, otherwise use the autosuggest filter.

The following users should have access to this filter:

• Admins
• Managers
• Subeditors
• Assistants

This filter should not appear unless at least one category has been configured in the journal, press or preprint server.

Who is asking for this feature?
Ubiquity Press, cc @salmanm2003.

[NateWr]

PRs (from @salmanm2003):
#6814
pkp/ui-library#145

[salmanm2003]

@NateWr the test is running here:
pkp/ojs#3064

[salmanm2003]

@NateWr the test is done, here is the result:
https://travis-ci.com/github/pkp/ojs

[NateWr]

All merged, thanks @salmanm2003! (It looks like the tests timed out, but I can see from the logs that they ran ok right up to the end, so pretty confident we're safe here.)

[NateWr]

Adding a note here, so we don't forget, that this will need to be backported to stable-3_3_1 once we've begun work on that branch.

[NateWr]

I've cherry-picked this feature into our new stable-3_3_1 branch so it will go out with the first 3.3.1.x release.

[salmanm2003]

Thanks @NateWr