Integrating TrustKit Framework

[jleandroperez]

Description:

This PR wires TrustKit into Simperium: we're replacing SocketRocket former pinning mechanism.

Testing scenarios below.

Needs Review: @roundhill @astralbodies

Thanks in advance!!!

Scenario: Pinning Disabled!

1. Clone both, Simperium + Simplenote repositories
2. Map Simplenote to your local Simperium checkout: pod 'Simperium', :path => '../simperium-ios/'
3. Pod install please!
4. Run Simplenote

Verify that no TrustKit legend shows up in the console. Sync'ing should work seamlessly.

Scenario: Pinning Enabled

1. Repeat steps 1-3
2. Open Simplenote's SPAppDelegate.m (method setupSimperium) and add this line: [_simperium setCertificatePinningEnabled:YES]
3. Run Simplenote

Verify the console logs. TrustKit should get initialized, and sync'ing should be working fine.

Verify Signatures!

1. Extract the PEM:
   openssl s_client -showcerts -host api.simperium.com -port 443
2. Save the first certificate *.simperium.cominto a .pem file.
3. Calculate the Public Key Hash
   ./External/TrustKit/get_pin_from_certificate.py certificate.pem
4. Verify that the key included in SPEnvironment.m matches

[astralbodies]

Appears to work wonderfully, @jleandroperez!

[jleandroperez]

Thank you sir!!