Forth Beta - More Fixes and Improvements

Description:

The next step in cleaning up and getting the code-base ready for becoming public in the near future.

Changelog:

• Improve the experience when logging in with the wrong account.
• Changed share wording to sync instead.
• Show sync errors with error popups in the GUI.
• Update in-memory login credentials when changing password or username.
• Added support for up/down arrows and enter to execute for username and password change entries in settings.
• How a popup telling the sender if the sync completed.
• Switch from activity wording to exercise.
• Clear the sync code on successful sync.
• In general a better sync experience for users.
• Improved file handling and better error messages (breaking change).
• Fix a couple security issues brought up by gosec.
• Move theme select to beginning to hopefully fix windows weirdness.
• A bunch of spelling fixes.
• Update fyne-cross to v1.4.0.
  • All binaries are now built with Go 1.13.8 over the 1.12.x series.
    • This means that MacOS 10.11 El Capitan is the minimum supported version.
    • Defer uses in the codebase should be around 30% faster.
• Updated fyne to v1.2.3 for a bunch of fixes.
• Switched from shell scripts to makefiles for common operations.
  • Added make check command for running gosec, misspell and gofmt for major checks over the whole codebase.