Prettify Pie Chart GUI

[qreoct]

Updated pie chart such that it looks like the mockup

• Mouseover on the pie chart will show the label
• Currently, pie chart re-renders on every command (in MainWindow::executeCommand()). Added a boolean isLogHours to CommandResult to represent whenever a command has modified the hours. Checking this boolean ensures that the pie chart doesn't keep re-rendering on every command
• Clean up XML and css for pie chart
• Added theme colours for pie chart for all themes

Part of #82

[codecov-commenter]

Codecov Report

Merging #131 (72117a7) into master (3e845e1) will decrease coverage by 0.37%. The diff coverage is 14.28%.

@@             Coverage Diff              @@
##             master     #131      +/-   ##
============================================
- Coverage     65.82%   65.44%   -0.38%     
- Complexity      633      634       +1     
============================================
  Files            92       92              
  Lines          2323     2338      +15     
  Branches        288      288              
============================================
+ Hits           1529     1530       +1     
- Misses          712      726      +14     
  Partials         82       82              

Impacted Files	Coverage Δ
.../java/seedu/address/logic/commands/LogCommand.java	0.00% <0.00%> (ø)
src/main/java/seedu/address/ui/InfoDisplay.java	0.00% <0.00%> (ø)
src/main/java/seedu/address/ui/MainWindow.java	0.00% <0.00%> (ø)
...va/seedu/address/logic/commands/CommandResult.java	84.21% <80.00%> (-4.03%)	:arrow_down:
...java/seedu/address/logic/commands/ExitCommand.java	100.00% <100.00%> (ø)
...java/seedu/address/logic/commands/HelpCommand.java	100.00% <100.00%> (ø)

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