Tags: support creating fixed collections of files / patterns / entities

[bolandka]

Additional tags may to date be inserted anytime. This will change collections generated by selecting tags and there is no way to define a fixed collection.

• 2 different types of tags: free form (current tags) + immutable collection tags?
  collection tags: define a collection, persist collection with uri, assign a set of collection uris as collection tags to the files / patterns / entities
• usage of Timestamps?

[kba]

We have these options now, tags can be specified for JSON import and for executions, as well as for uploads. We just need to document our best practices here.

[bolandka]

ok, lets do this here: https://github.com/infolis/infolis-web/wiki/Best-practices-for-using-tags