Consistent use of colors in the app

[Nekhelesh Ramananthan]

This bug report is to discuss the use of colors in uNav. Feel free to give your opinions. Currently in uNav we have colors displayed in the map and in buttons (Start, Overwrite, Add etc). I think we can be more consistent about which color we use and use them to aid the user. Here are a few examples,

1. All positive actions like "Add", "Edit" should use UbuntuColors.green. Negative/Critical actions like "Overwrite" use UbuntuColor.red

2. Remove all uses of UbuntuColors.aubergine color in uNav. That color is not recommended by the canonical design team to be used in apps. uNav uses it in the navigation panel, and as the background of the share button.

3. The "Center" header button should be "lightblue" when searching for the user location. It should be Green when it is disabled (user location is found). It should be "orange" when the user location is incorrect and enabled. Colors are more easily identifiable by the user. Currently uNav adjusts the opacity value which is not very visible when using it outside in the sun.

Summary: Colors are powerful indicators that help the user identify the state of uNav. Let's be more consistent on how we use them.

If there are any uses that I missed, please feel free to mention it in the comments or add them to the bug description.