Mhd/layer contents integration

[mhdostal]

Included in this PR:

• LayerContents component based on this design. Note that the title and title icon for both the Layers and Bookmarks view is under design review and not included here.

• Inclusion of an "Extras" button in the right side of the app's title bar which displays an AlertViewController allowing the user to select either Layers or Bookmarks.

• Integration of the LayerContents component in DataCollection.

• Integration of the Bookmarks component from the Toolkit (and inclusion of the Toolkit as a submodule).

Extras alert:

Layers:

Bookmarks:

[mhdostal]

@philium - I'm done making the suggested changes and addressing comments, so please give it another look.

The outstanding issues:

• any potential renaming/moving of the DataSource class
• LayerContentsTableViewController issues: Done/Cancel button and TableViewCell constraint issue
• Find a strategy to eliminate unnecessary loading of tableView data.

Thanks again for your review, it really helps make the code better.

[mhdostal]

@esreli, @philium I've addressed all the comments. Unless I missed something, the only outstanding item item is:

~- potentially show a title and "Done" button when displaying either the TOC or Bookmarks VC.~

[mhdostal]

@esreli I added the code to adjust the state of the extras button. Can you take look and make sure it's OK? One thing I wasn't sure about is the selectedFeature enum takes a Bool; I've added that item in the check twice:

mapViewMode == .selectedFeature(featureLoaded: false) ||
mapViewMode == .selectedFeature(featureLoaded: true) ||

[mhdostal]

@philium - can you give this a final(?) look?

[mhdostal]

@philium, @rolson I made the changes requested, please have another look.

[mhdostal]

@philium - Awesome, thank you for all the help!

[philium]

@mhdostal You're welcome! I'm happy to help.

[mhdostal]

@rolson Thanks!