Fixes for Imagery Snapshotting #3963

[charlesh88]

Fixes #3963. Changes and refactoring for imagery Snapshotting to cope with html2canvas shortcomings.

Todos

• Fix linting.
• Make sure test code in Compass.vue is acceptable; change or remove if not.
• Make sure tests aren't broken.
• Add testing notes to original issue.
• Add changes overview to this PR.

Changes

• Update to latest version of html2canvas 1.0.0-rc7;
• Better sizing and positioning for compass rose element;
• Compass rose rewritten as SVG for compatibility with html2canvas;
• Imagery view now hides local controls, pause button and prev/next arrows when taking a Snapshot;

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Author Checklist

• Changes address original issue?
• Unit tests included and/or updated with changes?
• Command line build passes?
• Has this been smoke tested?
• Testing instructions included in associated issue?

[akhenry]

Reviewer Checklist

1. Changes appear to address issue? Y
2. Appropriate unit tests included? N/A - Visual fixes
3. Code style and in-line documentation are appropriate? Y
4. Commit messages meet standards? Y
5. Has associated issue been labelled unverified? (only applicable if this PR closes the issue) Y