Portal to be aware of task recover/restart capabilities

[natacha-beck]

The Portal doesn't know which tasks are restartable or
recoverable, so it provides all the buttons at all times
in the task control panels. Capabilities not implemented
are triggered and the Bourreau Worker just ignore them
and return the task to it's original state.

The portal should have a way to know what capabilities are
implemented on the Bourreau side.

Related to : 1120, 1119, 706, 1105 (all in redmine)

Comments:

• Pierre: The capabilities could simply be added to the task's class'
  properties() method.
  Nick mentioned that another capability that the portal shoud
  be aware of: whether or not tasks require read/write or read only
  files. Right now the interface refuses to launch tasks selected
  on read only files, even for tasks that only read from them.
• Angela: Output files generated from running a task are by default Read Only files. Read Only files cannot by processed by tools, instead files must be selected and they must be converted to Read/Write by the user. This is cumbersome, especially when using conversion tools such as Dicom to Minc where a users' intention is usually to process those output files using a Scientific Tool such as CIVET. Users who launch a task should have Read/Write permissions on the output files generated by those tasks

[remibernard]

Would it be enough to just add the relevant properties to the properties method as mentioned, disconnected (code-wise) from the actual task capabilities? (i.e. you could have discrepancies between the task's properties method and its actual implemented capabilities).

Or is a more robust (but much more complex) solution in which the portal checks if the bourreau task has the relevant capability required?