feat: Built-in automatic update script

[4ntsy]

This P.R

fix:

• url of render markdown in textview (error presented with the .set_data method)
• sudo request in self-update script install.sh

feat:

• run the auto-update only if it is not a repository (git, copr or ppa), as they already guarantee the update
• built-in self-update on VTE
• improve dialogs

for the next release change the version in /p3/app/updater/__init__.py