Add pdf retrieval
code cleanup
Add log file retrieval
Add working directory cleanup action
Refactoring: use custom UserInfo type

For the moment the `common.UserInfo` type is just an alias for the
`sohva.UserInfo` type. But this may differ in the future. It does not
cost anything to use an alias here in this case, and make future
changes easier (when the code base will be much much larger).
more work on compilation activator

the compilation stuffs are deployed only when the synchronization server
is registered
Persist paper files before compiling