Valama: Support default files to open at initial project loading.

 * "opened-files" key is supported for project files but won't get rewritten
   to file. So this is only relevant on very first project load up (which is
   loading from template). Partly solution for #61 (1).
   TODO: Support this for templates only and not for normal projects.
 * No layout support for srcdock at the moment but this would fully fix the
   #61 (1) issue.