Adds check to prevent apps from including 'evd-transport.h' directly
tests: Minor updates in old tests
Adds implementation of Deferred/Promise pattern, EvdDeferred and EvdPromise
tests: Adds unit test for the new Promise feature, covering 100% of the API
build: Simplifies git ignore file under /tests
tests: Improves test-promise to add more assertions and increase coverity
Makes EvdDeferred a boxed type
Fixes error in parent object and class of EvdPromise, result from copy&paste
doc: Adds annotation and documentation to EvdDeferred and EvdPromise

Pending to add a couple of code examples.
Fully removes 'selector' property of EvdWebTransportServer
build: Forces TESTS_DIR defined variable to be an absolute path
tests: Updates the expected output of a test case in test-dbus-bridge