Use KeenClient library as a static liabrary

Libraries/libKeenClient.a should be generated as follows:
$ cd KeenClient
$ xcodebuild -sdk iphoneos
$ xcodebuild -sdk iphonesimulator
$ lipo -create Release-iphoneos/libKeenClient.a Release-iphonesimulator/libKeenClient.a -output ~/git/td-ios-sdk/Libraries/libKeenClient.a
Add Rakefile for build
Add TreasureData.xcworkspace
Fix Xcode build setting (removed -lPods)
Separate libKeenClient.a into for device and simulator
Remove workspace
Ignore TreasureData.xcodeproj/project.xcworkspace/xcuserdata
Add 'rake build' to create static library
Add uploadEventsWithCallback() instead of uploadEventsWithBlock() for error handling
Update header files
Remove unused headers
Update project files
Fix Rakefile
Add InitializeEncryptionKey()
Remove unused task
Merge branch 'use_forked_keenclient_with_3rdparty_pod'