Read desktop files inside AppImages

[probonopd]

Remaining part from #26 (comment):

% chmod +x ~/Downloads/Telegram_Desktop-x86_64.AppImage 
% ~/Downloads/Telegram_Desktop-x86_64.AppImage --appimage-extract
% cat squashfs-root/telegram.desktop
(...)
MimeType=x-scheme-handler/tg;
(...)

So, when encountering an AppImage, then "the system" (I still need to decide which component) needs to place the link to ~/.local/share/launch/MIME/.../ based on the information in MimeType= in the .desktop file inside the AppImage. (This already happens for .desktop files which are not inside AppImages.)

Possibly we can use the new libsqsh library by @Gottox for this. It looks promising and is under a permissive license.

• Support squashfs files that start at an offset Gottox/sqsh-tools#34

[probonopd]

In https://github.com/probonopd/Filer/ I have implemented AppImage squashfs reading using libsqsh; in the current architecture something like it would also need to be done in launch which populates and manages the launch "database".

[louies0623]

It should automatically detect all Appimages in the hard disk and display them on the list. It should allow people to choose the software to be executed by default from the folder, as shown in the figure.
image