Added ability to create "loader apps" for use on Main Menu

[ESurge]

What's new

Loader App

• It's a dummy app created for the purpose of attaching an application.fam file to use with Main Menu.
• I added a link variable to the application.fam file. It's used to specify the FAP file location needed for loading

Loader.c

• Changed loader.c to incorporate the application.fam link variable change which lets any FAP be on the Main Menu with the use of a "loader app"
• This removes the hard coded app loading (Clock/iButton/U2F) and creates it dynamically

Note

• If no link variable is specified in application.fam, it's automatically set to NULL which is then ignored by loader.c when launching the app.

Verification

• Create a dummy app using clock_loader, ibutton_loader, or u2f_loader as an example.
• Ensure the proper application.fam details are filled in, with the location of the FAP file needed for loading.
• Ensure loader_app is included in Main/applications.fam file
• Build
• Test if app shows up on Main Menu and loads FAP correctly.
• Also test if other apps still work correctly.

Checklist (For Reviewer)

• PR has description of feature/bug
• Description contains actions to verify feature/bugfix
• I've built this code, uploaded it to the device and verified feature/bugfix

[RogueMaster]

Thank you, that is a lot less code than before and this will let us set as Favorites 😄