Fix #1593: Unneeded file cleanup/XCode cleanup

[iccub]

Summary of Changes

This pull request fixes issue #1593

Since the code changes is too big, please look at commit names to see what things have been deleted or changed.

Overall summary of changes:

What was deleted:

• UI tests
• Push
• Snapshot
• FF marketing tests
• Buddybuild SDK, was still bundled in the app
• Unused 3rd party code
• old extensions files and its entitlements
• FF’s settings bundle
• Account scheme
• FF’s CI files: danger, code coverage tool

Folder/Group fixes
Certain folders were not linked in XCode and were still set as groups.
Also some files were placed in wrong location but still linked to folders
For example TabEventHandlers.swift was sitting in Client folder, but in XCode it was showing in Client/Helpers.
For such cases I moved the files accordingly

The only group type of folders left are Config, Frameworks and Products

New Config group.
It contains npm, carthage and other config files for quick access in xcode.
These files were but moved but only added as references.

Please squash all commits when merging, if something is wrong with this PR it will be easier to revert all changes at once

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Test Plan:

Screenshots:

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • release-notes/(include|exclude)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue is assigned to a milestone (should happen at merge time).

[jhreis]

Couple questions:

1. Does this make it any more complicated for us in the future to enable UITests if we want, or is this solely the removal of the literal FF UITests?
2. Do we want to implement codecov? Maybe something we can discuss at a later point, so removal of the file is probably not an issue.

[iccub]

1. This is removal of UI tests and their framework for UI tests based on ScreenGraph
   FYI the screengraph ui test stuff is now a separate framework https://github.com/mozilla-mobile/MappaMundi and if we would like to go this route it's better to use this newer approach

2. I would add it later, we have some ideas for CI improvements, like blocking merging if WIP string is presented