Case insensitive tags within each module

[Silvernitro]

Closes #148

As reported, we currently allow case-sensitive tags to be added to a single module, i.e. "foundation", "Foundation", which is confusing since the find command is case-insensitive.

Changes

• Tweak ParserUtil.parseTags to only add the first occurrence of a tag amongst duplicates. E.g. "core", "Core", "cOre" will only result in "core" being added. Also added a test for this.
• Minor refactoring to GradPad class's addModule and setModule methods. They duplicate the same code to replace tags so I've extracted that out into a getModuleWithReplacedTags fxn.

[codecov-io]

Codecov Report

Merging #170 into master will increase coverage by 0.02%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #170      +/-   ##
============================================
+ Coverage     75.40%   75.43%   +0.02%     
- Complexity      565      567       +2     
============================================
  Files            93       93              
  Lines          1720     1722       +2     
  Branches        175      176       +1     
============================================
+ Hits           1297     1299       +2     
  Misses          341      341              
  Partials         82       82              

Impacted Files	Coverage Δ	Complexity Δ
...in/java/seedu/address/logic/parser/ParserUtil.java	96.66% <100.00%> (+0.37%)	11.00 <0.00> (+1.00)
src/main/java/seedu/address/model/GradPad.java	83.33% <100.00%> (-0.39%)	17.00 <1.00> (+1.00)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update af938e3...215e803. Read the comment docs.