Improve Help Window UI

[Bonzzz3]

Description

Improve help window UI and make slight changes to main window UI

New features added

• Changed default colour to match colour scheme of main window's UI
• Enable expansion of window and columns
• Tweak styles such as text alignment, font size and font colour
• Updated User Guide with new help window screenshot

104

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/main/java/seedu/address/ui/HelpWindow.java	0.00%	2 Missing :warning:

Files with missing lines	Coverage Δ	Complexity Δ
src/main/java/seedu/address/ui/HelpWindow.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)