Revise action button colors

[jmaferreira]

The grey color is not working out for me. It may be confused with the disabled button.

I recommend using 4 colours:

1. Grey for disabled
2. Green for the main creation actions (e.g. NEW)
3. Red for destroyers (e.g. delete)
4. Blue for all the others

Some ideas or color button paletes.

[luis100]

@jmaferreira is this a priority? if not I would recommend postponing to another sprint.

Also, there is a way to make colors easier to change by using GSS instead of CSS, see #521

[jmaferreira]

1. It is not a major priority. It can be postponed 2. GSS will not enter this version of RODA.

[luis100]

Done