[10] Added help screen

[qhen143]

Ended up being more difficult (for me) than intended. Resolves #10 .

Changes:

• Created help screen component and wrote up a html+css from scratch.
• Filled the help screen with descriptions and/or instructions of how to use features of the application.
• Reduced scrolling required to view the page through the use of accordion/drop down elements.
• Visual cues/animations when opening/closing a description. 👀
• Added routing to help screen component and back button.

To test:

1. Click on the 'help' tab at the top.
2. Click on 'VisualGit: A visually oriented Git client'. Expected: Help page is opened.
3. Click (and read) all the blue headings. Expected: When the labels are clicked, the corresponding descriptions are revealed.
4. Click them again to check all the corresponding descriptions are hidden. Expected: When the headings are clicked, the corresponding descriptions are hidden.

To test the back button:

1. Navigate to any page.
2. Click on the 'help' tab at the top.
3. Click on 'VisualGit: A visually oriented Git client'.
4. Press the 'Back' arrow. Expected: The user is returned to the page from 1.
5. Repeat 1-4 with a different page.

[qhen143]

Most recent push was just a rebase to #217 .