Bugfix: number of tag catgories defined

[AriellaCallista]

Intended functionality: users should be able to define up to 3 more categories on top of the 3 predefined categories that come with JABPro. Note that the 3 predefined categories were not documented in v1.3 UG BUT this has been the behaviour since v1.3 due to the use of sample data/tags in JABPro and hence this was NOT a behaviour change.

Bug: users can only define up to 2 more categories if they have uncategorised tags (created from doing edit or add with a tag that hasn't been created)

Fix: ignore uncategorised tags when counting the number of tag categories that the user has made so far since they technically never intended to create the uncategorised "category".

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (bfb6901) 73.12% compared to head (3deaffa) 73.10%.

Files	Patch %	Lines
...seedu/address/logic/commands/CreateTagCommand.java	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #228      +/-   ##
============================================
- Coverage     73.12%   73.10%   -0.03%     
  Complexity      916      916              
============================================
  Files           126      126              
  Lines          3059     3060       +1     
  Branches        370      371       +1     
============================================
  Hits           2237     2237              
  Misses          721      721              
- Partials        101      102       +1     

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[MadLamprey]

LGTM