Define behavior & implement pause() & unpause() functions

[cloudvenger]

Description

Define behavior & implement pause() & unpause() function

Definition to answer :

• Do we disable deposit ?
• Do we disable withdraw ?
• Do we disable computation reward ? or do we set price to 0 until unpause ?

Acceptance Criteria

• Definite business / field behavior wanted
• Implement behavior in pause() & unpause()
• Tests (unit & integration) pause() & unpause()