Add autofocus in prefix field, so that it gets the focus on page load
When DeviceStorage is not available, display only one "input type=file multiple", in which the use must select all the archive files. It's quicker and easier than selecting each type of file individually. Fixes #28
Also implemented reading all the kind of files of an archive : titles_search.idx and coordinate files (both unused for now)
Fix on autofocus of prefix field.
We don't want it to be focused on page load, but each time the archive is selected (either through DeviceStorage or manual file selection)