[FEATURE] [FRONTEND] Styles Cleanup

[0xMurage]

Describe the user story:

Although Wikonnect utilizes the Sass preprocessor, the functionality is not fully exploited at the moment.
The is no consistent use of colors/themes across various components making it difficult to handle #94.

Component-specific styles should utilize CSS modules provided by ember-css-modules package.

Tasks (where applicable)

• Provide colors via centralized variables
• Centralize teach and learner color themes - to be swapped with css variables

Acceptance Criteria

On all UI components,

• Current UI/UX functionality should be maintained
• Current UI look and feel should be maintained