Don't put echoSettings in build.sbt anymore and other echo installer fixes

 * make the "have we added this" flags past-tense not -ing
 * we set addingEchoFile when we added the background file,
   and addingBackgroundFile when we added the echo file, fix.
 * we used editedBuildFile for two purposes, change it to
   addedForkInRun and drop the code that added echoSettings
 * fix the filenames in the echoInstaller.html modal to reflect
   current actual filenames
 * add TODO that using applicationReady to compute echoReady
   is broken
Merge pull request #744 from typesafehub/wip/havocp-fix-echo-settings

Don't put echoSettings in build.sbt anymore and other echo installer fix...
Bring back the actors inspector
Inspect styling and behaviours
Complete refactoring for actors errors
Echo settings are now automaticaly loaded