tns run command to watch for changes by default

[tzraikov]

Currently when executing tns run command you should pass the --watch option in order to start watching for changes. We will change this behavior so that when you execute tns run command the watch to be on by default.
If you don't want to watch, we will provide a --no-watch option.
If you want to rebuild the application explicitly, we will provide the --clean option

The deploy, prepare and build commands will not be changed. The livesync command will be deprecated in 2.5 and removed in 2.6.
We should update the docs accordingly.

[vchimev]

Additional:
In order to run the app and release the console/terminal, --justlaunch option should be used.

Summary:
https://github.com/NativeScript/nativescript-cli/wiki/Workflow-commands-spec#run