Add VolumeClaim scheduler, Volume controller and VolumeClaim controller

[afritzler]

Proposed Changes

• Schedule VolumeClaim to reference a matching Volume
• Add Volume controller to handle Volume phases
• Add VolumeClaim controller to handle VolumeClaim phases

Test cases:

VolumeClaim scheduling

• Matching Volume and VolumeClaim based on Resource requests
• Do not match if StorageClasses are different
• Do not match if the Resource requests of the VolumeClaim are higher than offered by the Volume
• Match a VolumeClaim if two Volumes with different Resources are available

Volume

• Bind volume to matching claim
• Unbind volume if the claim disappears

VolumeClaim

• Bind a claim to a matching volume
• Mark a claim as lost if the volume gets deleted

Fixes #294

[afritzler]

The unit tests are a bit verbose at the moment. They probably need some refactoring/cleanup.