[Icons] Tweak appearance to match mock-ups

This follows up on prior pull requests for nasa/mct#138 and advances nasa/mct#145 in the following ways:

* Adjust appearance (mainly spacing) of view switcher and surrounding buttons to more closely match provided mock-ups
* Removes icons which predate the current icon set (and do not match, particularly when processed)
* Consolidates some code related to the Refresh button to make future re-use easier



Wrote or re-wrote unit tests (Y/N): Y
Ran entire suite of unit tests successfully (Y/N): Y
Verified bug fix with the described replication steps or verified the implementation meets the requirement cited (Y/N): Y
Code coverage requirements satisfied (new code=80%, changed code=at least as high as existing) (Y/N): Y
Code review date and attendees: Code review by pull request
Describe potential impact on other areas of the code: Center pane views, inspector, icons
Describe any test prerequisites for this fix (e.g., restart the database): N/A
For bugs marked "Regression - Yes", describe the cause of the regression: N/A
Did you modify any pom.xml file? If yes, did you thoroughly document your changes and reasons? N