Allow Custom Install Locations

[ImpossibleReality]

Describe the feature request
Users should be able to specify a custom install location, not only for linux, but also for mac and windows. Many users (like me) install apps in non-default places, like ~/Applications/ for user-only apps.

Expected behavior
Maybe a --install-path flag in the injection script allowing custom install paths.

[MulverineX]

It is not possible with the default windows discord installer to install to a custom directory. Portapps has support for (portable) discord, but they only have built for stable and PTB, which Powercord no longer supports (it requires Canary).

Good idea for macOS though.

[rosegayming]

It is not possible with the default windows discord installer to install to a custom directory.

@MulverineX There are ways other than Portapps like scoop to install it on windows so there still is a point.

[MulverineX]

Oh okay. Fair enough.

[ImpossibleReality]

I opened This PR: #426 for MacOS.