Library: Restyle the action buttons for Sakai tools (Primary and Secondary actions)

Following Kyle Blythe recommendations in SAK-31204:

Currently, all actionable buttons in several tools are styled the same, with blue background and white text. This makes it difficult to scan through and identify the primary action (e.g., "Post" or "Submit"), as all of the buttons look the same.

We recommend following the approach used by Google and other apps, wherein the "primary" action is styled with a background color, and all other actions be styled in a light grey so as to be less attention-grabbing.

The main objective of this Jira is update all the Sakai tools to follow this convention, like this example in Assignments:

OLD:

PROPOSED: