Making JSON-RPC accept more content types

According to the RFC for JSON-RPC over HTTP at
http://www.jsonrpc.org/historical/json-rpc-over-http.html
"Content-Type SHOULD be 'application/json-rpc' but MAY be
'application/json' or 'application/jsonrequest'"

This patch fixes HTTPJsonRpcHandler to allow for any of those three
content types when accepting JSON-RPC HTTP requests.

This also fixes compatibility with the popular Python library jsonrpclib
which uses the application/json-rpc content type.
[codegenerator] Helper.groovy: fix typo
[codegenerator] Helper.groovy: add support for class variables
[codegenerator] python: extend IN typemap to support int, double and float
renderer: replace render buffer indices with queues
renderer: simplify code by always maintaining one front buffer
renderer: remove now pointless GetNext(Decode/Render) function
renderer: name present buffer structure to be able to reference it
renderer: store bypass format in rendermanager instead

The present method will be overwritten on each flippage
renderer: drop copies of variables, use queue data directly
renderer: grab presentlock in AddVideoPicture
DVDAudioCodecFFmpeg: Grow the resampling buffer as needed instead of allocating it an arbitrary big size.
DVDAudioCodecFFmpeg: Remove write only assignment.
[rbp/omxplayer] do not reopen the resample context for each frame.

I think this doesn't tend to happen on Pi now, as AV_SAMPLE_FMT_S16 and AV_SAMPLE_FMT_FLTP bypass the resampler,
but best to fix it if some obscure codec returns something else.

See #2873
DllAvFilter: Always include libavfilter/buffersrc.h for av_buffersrc_add_frame.
Merge pull request #2881 from popcornmix/avoid_resample_init

[rbp/omxplayer] do not reopen the resample context for each frame.
Added CFileItem::FillInMimeType() and make GetMimeType() respect const qualifiers.

Before, the MIME type would only be resolved if GetMimeType(true) was called, which is potentially blocking. Now MIME types will be resolved from the file's extension without possibly blocking the thread. See doxy of CFileItem::FillInMimeType() for more info.
Revert "Merge pull request #2809 from jmarshallnz/no_skip_for_you"

This reverts commit c5a85f72b6f685be832d4e3a43328de49baabf03, reversing
changes made to e9aed1d645158647aa2006ac4b2d2d18a3d1ecbf.
Only allow prev-next chapter jumps outside of active playlist
Move player action handling out of GUIDialogVideoOSD and GUIWindowFullScreen into Application