Merge pull request #853 from gontofe/master

Prevent promptWifiOn() needing to be called twice and refactor OTA update fetch/version check
refactoring: use Document API getCoverPageImage to get cover image
Merge pull request #854 from chrox/screensaver

refactoring: use Document API getCoverPageImage to get cover image
Only use registered file types in search
Merge pull request #855 from WS64/master

Only use registered file types in search
Bring back the two KOBO variables for the light

This should close #856.
Although still closed I will check this one back with someone from the German forum, I hope this also closes #822, but there might be still some problems with the light-bug introduced in Kobo's firmware 3.5. But since 822 is already in the state closed we can leave things as they are for now and I will reopen 822 if necessary.
Merge pull request #857 from WS64/master

Bring back the two KOBO variables for the light
Set minimum light to 0 instead of 1
Merge pull request #860 from WS64/master

Set minimum light to 0 instead of 1
fix performance issue of screensaver on Kobo
now loadDocument will not render the document and getCoverPageImage will
be much faster.
Merge pull request #861 from chrox/screensaver

fix performance issue of screensaver on Kobo
don't share info field in document
We may have multiple documents opened simultaneously, such as in
screensaver mode the current document is opened twice, it's better
to keep seperate info table for each document.

This should fix #858. When a credocument is opened for screensaver to
get the cover page, the total pages info is set to 1(strangely enough),
before this fix this total pages is shared with the reading document
so the progress bar will get a progress percentage well beyond 100% and
rendering the progress bar out of the boundering box as shown in #858.
Merge pull request #862 from chrox/fix_858

don't share info field in document
register opened document in documentregistry
so that when calling getCoverPageImage in screensaver mode
the document won't be opened again. This should avoid a lot of
problem such as messing up style and options described in #863.
Merge pull request #867 from chrox/fix_863

register opened document in documentregistry
issue error directly when doc is malformated
This should popup a message saying "No reader engine for this file"
instead of a crash when document file is malformated.

This should fix #868.
Screensaver repair

Single picture as screensaver was not displayed anymore after the last update
minor code optimizing
Merge pull request #871 from WS64/master

Screensaver repair
Merge pull request #870 from chrox/fix_868

issue error directly when doc is malformated