Allow the admin to indicate that task can modify its input in a ToolConfig

[prioux]

Right now the CBRAIN task launching interface will refuse to launch a task when:

1. the user has selected a file that they don't own
2. the file's group_writable attribute is set to read-only
3. the task doesn't say explicitly that it doesn't modify its inputs

The behavior of point 3 is the default. A task can inform the framework that it doesn't modify its inputs by having either:

• task_properties :readonly_input_files in portal/taskname.rb (standard integration)
• "custom": { "cbrain:readonly-input-files": true } (Boutiques integration)

Given that often integrators forget to set these properties, the admin should have the ability to override the behavior directly in a ToolConfig (or maybe directly at the Tool level?). This would be provided by a simply checkbox in the ToolConfig form, associated with a new boolean attribute:

  [ ] Does not require write-access to inputs

[prioux]

The code that makes the check is in the tasks_controller.rb

    # Filter list of files as provided by the get request
    file_ids = params[:file_ids] || []
    access   = @task.class.properties[:readonly_input_files] ? :read : :write
    @files   = Userfile.find_accessible_by_user(file_ids, current_user, :access_requested => access) rescue []
    if @files.empty?
      flash[:error] = "You must select at least one file to which you have write access."
      redirect_to :controller  => :userfiles, :action  => :index
      return
    end

[prioux]

If the checkbox is not set in the tool config (which should be default), then the value of the task integration code is used, as normal, which can mean yes or no.
If the checkbox is set, the value of the task's integration is ignored and the task is considered to not modify its inputs (meaning the find_accessible_by_user() with use :read )

[prioux]

Make sure the migration sets a default value to 'false' in the table.