Dupllicate Tags

[omardoescode]

I noticed that it's possible to create duplicate tags that all have the same name on the web version

To reproduce the bug:

1. Write a tag name in the tag input
2. Click Enter
3. Write the same tag name in the tag input.
4. Click Enter

In addition, you can open another task that didn't have this tag

1. Write the same tag name
2. Instead of using arrows or cursor to click on the previously created tag, click enter immediately to generate multiple tags with the same name

Browser: Mozilla Zen 1.15.5b
OS: Arch LInux

[omardoescode]

If feasible, I would like this issue to be assigned to me

Suggestions:

1. Create a unique constraint/index on the mongodb tag model (Optional)
2. Fetch tags and check if the tag has been created before