Tagging auto-completion

As person using the dwyl app
I want to have auto-completion for tags
So that I can see all the tags available to me (which will help me categorise)
and make sure that I don't duplicate the tags that already exist

## Acceptance Criteria
+ [ ] In the 'Edit item' view, I now see all of the tags that are already associated with an item as coloured boxes/pills under the item (separate issue to be open for this UI)
+ [ ] There is a 'tags' text area where I can add new tags (this is still visible by default for now - when we have more tasks that can be performed with an item, this will likely become a button to choose specifically to add tags)
+ [x] Clicking into the tags text area opens a drop-down list of all the existing tags in alphabetical order
+ [x] As I type into the tags text area, the list narrows to include any tags that include that combination of letters
+ [x] I can touch/click on one of the options from the drop-down to select it as the tag to attach
+ [ ] I can also keep typing to add a new tag - once I finish typing I hit the '+ Tag' button and there is a check to see if the tag already exists. If not, a new tag is created and added to the capture