Move icon property to WebAppMeta

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Remove duplicate WebApp and WebAppMeta properties

data_dir and removable properties are now only in WebAppMeta

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Prefer use of WebAppMeta over WebApp

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>