USER STORY: Adjust all app colors/shapes

[blahosyl]

As a Developer,

I want to harmonize all visual elements of the app ,

so that the result is consistent and visually pleasing

Acceptance Criteria

1. Nav links & icons conform to color palette
2. In-text links conform to color palette
3. Backgrounds conform to color palette

Tasks

• [x] adjust logo

• [x] adjust favicon

• [x] adjust nav icons incl. hover

• [x] adjust links incl. hover

• [x] adjust app background

• [x] adjust button styling

• [x] adjust modal styling

• [x] adjust Signin form styling

• [x] adjust Signup form styling

• [x] adjust Task Create/Edit form styling

• [x] adjust ProfileEdit form styling

• [x] adjust Username form styling

• [x] adjust Password form styling

• [x] #136

• [x] set different styles for Submit & Cancel buttons

• [x] #137