According to the AppStream specification org.keepassxc is not a valid
id. The product name is missing. This results in failures if one tries
to validate the file and makes it unusable where validation is enforced.
Additionally it seems specification don't allow the `<icon>` tag with
component type desktop-application. I am not sure this tag is strictly
necessary. In any case validation tests require this to be removed.
Fixing both of these issues ensure the AppStream appdata is compliant
and works anywhere passing validations is a requirement.
Also provide some other fixes and improvements to the appdata.
Minor validation failures:
- Fix missing captions for screenshots (`appstreamcli`)
- Fix descriptions cannot start with `<ul>` tag (`appstream-util`)
Other enhancements:
- Add more URL types, but could not add donation type because "&" is not
allowed in the `<url>` tag and using "%26" causes
`appstreamcli validate` to fail.
- Add `<developer_name>`, which in cases such as KeePassXC is a team name.
