Prevent tag input field from changing height

Alternative fix for #1477 and remove use of px in the tag-input module. The main differences are:

* Ensures there is spacing between tags when wrapping onto a new line.
* Retains the larger hit area for the delete tag button (its fills the entire right side of the tag).
* Retains the bold "x" for deletion to distinguish it from the tag text.
* Ensures the "x" is not selected as part of the tag text.