Provide more eye sizes in themes and adapt the plugin size to the panel size
Currently the size of the plugin is fixed according to the chosen theme. As a result, depending on the size of the panel, the plugin may not fit in it or on the contrary may be too small.
Moreover, this does not allow to apply correctly a window scaling factor. As there is only one eye size available, the only thing to do to get a sharp image is to ignore the scale factor. So regarding the size of the plugin, this improves the above situation in some cases, but makes it worse in others.
Here is a patch that does this, but it's probably best not to apply it to master as it may appear as a regression to those who are used to using this plugin as is at 2x scale.