Rework SRT plugin to unify client/server and add features

Submitted by Roman Diouskine

Link to original bug (#796963)

Description

• Unify client/server for both, source and sink elements
• Add missing properties to improve SRT feature coverage
• Add ability to set SRT properties via URI
• Add rendezvous mode
• Add glib 2.54 compatibility
• Add optional reconnect with max reconnect retries feature to the source
• Allow overriding source message size and number of messages per read
• Improve SRT state handing in source and sink elements