Merge mozbuild files into tor-launcher.git

Step 1 of using TorLauncher with TBA is merging TorLauncher into tor-browser. As a side effect of this, we avoid rewriting it using the Webextensions API which provides limited functionality compared to the legacy XPCOM interface.

I see (at least) three options:

• Copy the current tor-launcher.git src/ directory code into tor-browser.git and maintain it in tor-browser
• Copy the entire tor-launcher.git repo into tor-browser.git as a nested git repo (preserving the .git/ from tor-launcher), continue maintaining tor-launcher.git but update the version in tor-browser.git by git pull from tor-launcher.git whenever needed
• Add tor-launcher.git as a git submodule

I'm currently favoring 2 or 3 because this means the other XPCOM/XUL apps can continue using it and we don't run into a problem with tor-launcher-in-tor-browser becoming out of sync with tor-launcher.git.

If we follow 2), then it adds an additional step whenever new code is merged into tor-launcher.git because then it will need to be pulled into tor-browser.git, too. One advantage of this is it simplifies the build process and tor-browser-build won't need a tor-launcher project. On the other hand, this means we'll need a new build flag for enabling/disabling including tor-launcher (otherwise tor-launcher will be included and run at startup by default, always).

If we follow 3), then tor-launcher remains a separate project that is cloned and integrated only when it is needed (much like it is currently at build time). This choice comes with the disadvantages of using a submodule, but it keeps the two repos decoupled.

From these three choices, it seems like using a submodule is the best choice, so we should merge the moz.build and jar.mn into tor-launcher.git.