Fixes failing dependency checks for extensions having a different package name and import name (for example ffmpeg-python / ffmpeg), which currently is causing the unneeded reinstall of packages at runtime.

In fact with current code, the same string is used when installing a package and when checking for its presence, as you can see in the following example:

> launch_utils.run_pip("install ffmpeg-python", "required package")
[ Installing required package: "ffmpeg-python" ... ]
[ Installed ]

> launch_utils.is_installed("ffmpeg-python")
False

... which would actually return true with:

> launch_utils.is_installed("ffmpeg")
True