Backend preferences

Schema for CARTA backend preferences (Version 2)

https://cartavis.org/schemas/preference_backend_schema_2.json
type	object
properties
backendConfigVersion	The version of this backend configuration
	type	string
	default	2.0
verbosity	type	integer
	enum	0, 1, 2, 3, 4, 5
	default	4
no_log	type	boolean
	default	True
log_performance	type	boolean
	default	False
log_protocol_messages	type	boolean
	default	False
no_frontend	type	boolean
	default	False
no_database	type	boolean
	default	False
no_http	type	boolean
	default	False
no_browser	type	boolean
	default	False
browser	type	string
	default
host	type	string
	minLength	1
	default	0.0.0.0
port	default	3002
	anyOf	type	integer
		type	array
		items	type	integer
omp_threads	type	integer
	default	-1
top_level_folder	type	string
	minLength	1
	default	/
frontend_folder	type	string
	minLength	1
	default
exit_timeout	type	integer
	default	-1
initial_timeout	type	integer
	default	-1
idle_timeout	type	integer
	default	-1
read_only_mode	type	boolean
	default	False
starting_folder	type	string
	minLength	1
	default
event_thread_count	type	integer
	default	-1
enable_scripting	type	boolean
	default	False
http_url_prefix	type	string
	minLength	1
	default