Update to JUCE 7 and CMake

[sudara]

@nholighaus asked me to publish this update somewhere. It's over on my fork but here's a PR in case there's a desire to merge it into the main repository (no worries if not).

The big picture changes are:

• Updates to JUCE 7.x (as a git submodule pointing to the develop branch)
• Updates to use CMake for building (based on my template https://github.com/sudara/pamplejuce)
• Creates an Assets target to stick all the svgs in
• Removes the deprecated juce header and adds appropriate includes and juce:: namespacing where necessary
• Migrates to use ltfat_complex_s** types from fftw_complex_s
• Updates some outdated ltfat function call names
• Fixed an issue with filterbank loading stalling out (on timer stop)
• Adds a .clang-format file

Things I didn't handle:

• ScopedPointer is deprecated
• Migrating from the HighResolutionTimer to vertical sync with JUCE's new VBlank support
• JUCE_MODAL_LOOPS_PERMITTED=1 which is deprecated, but needed for current implementation of file chooser
• Would be nice to build for all 3 platforms on GitHub Actions