Add tags to image collections

[MyleneSimon]

Description
Users would like to be able to add tags to their image collections, so that they can then filter and search by tags in the image collection list view.

Proposal
User should be able to add tags to collections, either by selecting existing ones or adding new ones. Image collection model will have a list of tags.
We will need new search methods in the ImageCollectionRepository as well to search by tags.