Add gas cost tests for common utilities, like auth, proxied calls, and permission changes

[sohkai]

Similar to #493, it would be interesting to have explicit gas cost tests on the following common overhead points in an AragonApp:

• isInitialized modifier vs. without
• auth modifier vs. without
• rentrancyGuard modifier vs. without
• Call through proxy vs. no proxy
• Cost of an isContract check
• Cost of initialize() with varying argument sizes
• Cost of accessing a constant value

And for the ACL:

• How much it costs to use createPermission() and grantPermission()