[Linux] os-release: unescape quotes / backslashes
The os-release specification states that single quotes, double quotes
and backslashes are supposed to be escaped with \. Unfortunately
I missed this in my original commit 7a9aa6f5d9ac8df1c79eb06ed63bce8af162c3ba.

http://www.freedesktop.org/software/systemd/man/os-release.html
Expose ACTION_FOO, ICON_TYPE_FOO and KEY_CODE_FOO to addons
Don't display blank SMB workgroups.
Implement seek for CDDA
[Fix] Event server code for remote mouse with event client protocol
Added JSONRPC.NotifyAll as a built-in function
Faster sorting of CFileItemLists, step 1

CFileItemLists are sorted by first construcing a SortItems object that refers
back to each CFileItem by index, sorting the SortItems object, then rebuilding
CSortItemList::m_items (a vector of pointers to CFileItems) by examination of
the sorted version of the SortItems object.

It might be more sensible, long-term, to sort m_items directly, but in the
meantime, there are a couple of simple ways to make sorting with SortItems
sufficiently efficient that it's not a problem any more.

Previously, SortItems was a vector of SortItem objects, held by value; each
SortItem was a std::map (implemented as a red-black tree) which ended up
being constructed and destructed as each element of SortItems was moved.
This patch changes SortItems to be a vector of pointers to SortItems instead.

Benchmarks for CFileItemList::Sort() on a Raspberry Pi with a library of
600 movies:
Before patch: 4.6 seconds
After patch:  1.1 seconds
Faster sorting of CFileItemLists, step 2

Each time a CFileItemList is sorted, multiple SortItem objects are
constructed and destructed. Each object is a std::map ,implemented as a
red-black tree with one node for each attribute (Field) upon which the
CFileItemList could conceivably have been sorted, even though for any given
SortBy, very few attributes are actually examined by SortUtils::Sort(). Worse
still, many of those nodes involve creating an associated fresh copy of a
string, with all the associated heap thrashing that entails.

This patch changes the various ToSortable methods to limit the number of
items in each SortItem's std::map to those actually required for performing
the chosen sort.

Benchmarks for CFileItemList::Sort() on a Raspberry Pi with a library of
600 movies:
Before patch: 1.1 seconds
After patch:  0.36 seconds
Fix typo in setup of sort-by-album-artist inherited from previous code
changed: Implement pausable priority and get rid of old method
changed: Use CJob::PRIORITY_LOW_PAUSABLE for (non-essential) image jobs
changed: Pause low priority jobs when loading/showing pictures
changed: Rename pausedType to something more suitable
fixed: Music playlist wouldn't progress with pending jobs (fixes #14574)
changed: Implement ChapterOrBigStep-actions and make previous BigStep-actions without chapter seeking
remove xbox system info
remove xbox from gui dialog
add subtitles extension list and allow to remove it using URIUtils::RemoveExtension
removed all methods related to loading string blocks into memory. afaik this is obsolete and not in use anymore.
fixed possible but unlikely overflow.