[Atom] Add readonly qualifier to some properties
[Atom] Add readonly qualifier to some properties

AgentME/DefinitelyTyped,rolandzwaga/DefinitelyTyped,AgentME/DefinitelyTyped,mcliment/DefinitelyTyped,georgemarshall/DefinitelyTyped,rolandzwaga/DefinitelyTyped,magny/DefinitelyTyped,markogresak/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,one-pieces/DefinitelyTyped,AgentME/DefinitelyTyped,borisyankov/DefinitelyTyped,dsebastien/DefinitelyTyped,borisyankov/DefinitelyTyped,dsebastien/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,magny/DefinitelyTyped