webserver: cosmetic refactoring
webserver: add support for If-Unmodified-Since HTTP header
webserver: add Cache-Control HTTP header to cacheable responses
webserver: handle Cache-Control: no-cache and Pragma: no-cache
webserver: use defines for HTTP header fields and values
webserver: silence warning
webserver: refactor IsAuthenticated()
[lang] update of internal addon language files
[lang] update of core language files
[lang] update of skin.confluence language files
[confluence]  [confluence] minor cosmetic to codec info background
BaseRender: Allow 1px wrong in aspect ratio to not do completeley refit the image
Merge pull request #5960 from FernetMenta/streams

dvdplayer: allow skipping streaminfo only for mpegts streams
Merge pull request #5955 from uNiversaI/patch-3

[confluence] minor cosmetic to codec info background
[keyboardlayout] Add Greek QWERTY

Greek QWERTY keyboard layout. All accented characters are under "symbol,shift+symbol". No space for the capital accented characters though.
Merge pull request #5967 from host505/patch-2

[keyboardlayout] Add Greek QWERTY
Revert to software decoding for AVC profile 578 as it is not handled by imx6 VPU
EGL: Add Quirk for display recreation
IMX: Announce EGL_QUIRK_RECREATE_DISPLAY_ON_CREATE_WINDOW to fix refreshrate change
Merge pull request #5966 from fritsch/imx-helix-ports