Fixes #1939

Changes:

• Added a Download all sketches button
• Added Download all sketches in English translation file
• Added new controller downloadAllProjectsAsZip
• Added a new library bundling function to handle library bundling in the case of multiple projects

Logic: I created a function called compileProjects that can merge multiple projects into one big project that treats all the projects as subfolders. This compilation follows the JSON format needed for the addFileToZip function to work and thus reuses the same method used for singular project. I also created a new function bundleExternalLibsForCompiledProject that handles bundling library files for the compilation. It adds specific library files to each project folder for that particular project.

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123