Add support for TryExec desktop entry

[mijorus]

Hi there,
I am the developer of Gear Lever, another popular tool to manage AppImages.

I just wanted to ask if you could add the TryExec directive to the desktop files that AppManager generates, as Gear Lever uses this information to list the currently integrated in the system.

In this way, users can switch between tools easier.

[kem-a]

Hi. Good luck with your project!

TryExec was causing issues to me. I noticed that some apps will fail to launch if that entry is present. I haven't investigated why, so I just removed it, but I can reopen this issue.

[mijorus]

I also saw that you are using X-AppImage-Homepage, it's a good idea.
I will add this to Gear Lever as well, so they can interoperate better