Leveraging the work done by nixpkgs maintainers

Right now I'm only focussing on required dependencies for Linphone
Desktop

Basic integration with direnv to get a compilation environment suitable
enough for running tests

    Handle dial out conference while there is already an ongoing conference:
    - the conference server will always initiate call in dial out conferences if there is no one yet established
    - clients that are already in a conference call will reject any new incoming call from the same conference server with a 486 Busy Here

    If a participant requests a video stream of another participant whose video direction is inactive or recvonly, then the conference server will reply with an inactive stream
    Remove label and ssrc from participants whose video is disabled
    Do not send separate notifys for changes of an ssrc and media capability or availability changes

Updated liblinphone to keep a ref on the LoggingService to prevent a crash that can happen sometimes if the JAVA object isn't held by the app

When renaming a file after a transfer, use system locale. The bug appears on Windows when it receives an UTF8 filename. The encoding should not depend of the application as it is related to the current system.
bctbx_file_open2 doesn't support unicode. Convert string when opening a stream.
Add custom encoding string convertions.
Fix Xamarin Nuget upload.

Add property [rtp] stun_keepalives to allow disabling stun keepalives. By default, they are allowed. Stun keep alives are used only when ICE is not available.

   Only list chatrooms that belong to the account that has just registered

Feature : Set another device while being incall for all platforms. - Restart the running stream when setting an audio device and if MS_AUDIO_CAPTURE_SET_INTERNAL_ID or MS_AUDIO_PLAYBACK_SET_INTERNAL_ID have not been implemented by the filter.

Updated liblinphone to fix an Android issue when app is configured with background mode & auto start at boot

- Replumb video graph if a filter changed its output format while not being in call. - MSMFoundation : Choose at best the requested resolution.

-Avoid building multiple time the nuget.
-Build both x86 and x64 for UWP.
-Compress into one file for all architectures.
-Write the nuspec from LINPHONESDK_UWP_ARCHS.
-Use UWP for UWP application.

Updated liblinphone to improve push notification process when Core was alive & network related tasks aren't necessary

Updated liblinphone to improve getDownloadPath request made to the Android platform helper each time a message is received

MSMFoundation : only validate a new format if it was set to the source.

factorize cache to ease re-definition to use multiple caches (gradle and ccache for example)

Move the Gradle directory to the working directory to allow cache creation

Added invitations update and cancellation information to PushNotificationMessage for iOS Service notifications