Move validation checks and cleanup checks outside of boot process

[prioux]

When the BrainPortal or Bourreau boots, some validations and cleanup steps are performed that are not necessary to do every time. Move them out so the boot process is faster. They steps shoudl be performed by rake tasks, or maybe triggered in the console, or with the interface, or all three. Optionally, these steps could be run in reporting mode only, or in active fixing mode.

• On BrainPortal: (file lib/portal_system_checks.rb)

• None

• On Bourreau: (file lib/bourreau_system_checks.rb)

• (Remove completely) old task work directories convention adjustments
• Check for existence of task work directories
• Check for consistent task archived flag
• Refreshing task workdir size
• Spurious task workdirs

• On both: (file lib/cbrain_system_checks.rb)

• Old SyncStatus object
• Old files in Cache