tags needs its own form_snippet to fix css class

[howff]

CSS includes form-control which causes incorrect layout.
In order to remove form-control we need a new form_snippet for tags; same as for text but without form-control.
Fixes #219
except only for tags not file format or other glitches.

[LukeTully]

@howff Did you find why this was? Is form-control used as the selector for the tag_string_autocomplete preset javascript? Seems like adding a class called "NOT-form-control" could be approached differently if we know what specifically is causing the issue.

[howff]

I didn't try too hard to find the exact cause, sorry it was a quick hack to get it working. I left the CSS in there and added the NOT prefix just to indicate where the fault lies, not because I want a class with that name. The effect seemed to be caused by the class appearing twice, once on an element which is underneath the element we want, and having the class applied to the top one caused it to be offset from the one underneath instead of hiding it.