Create Info.plist for resource bundles

Seems like the root cause of CocoaPods/CocoaPods#3310 is that we don't create a proper Info.plist for resource bundles, whereas Xcode does that. `Xcodeproj::Project.new_resources_bundle()` should create that so that the resource bundle is actually of the same form as those Xcode itself creates:

``` xml

CFBundleDevelopmentRegion
en
CFBundleExecutable
$(EXECUTABLE_NAME)
CFBundleIdentifier
com.contentful.$(PRODUCT_NAME:rfc1034identifier)
CFBundleInfoDictionaryVersion
6.0
CFBundleName
$(PRODUCT_NAME)
CFBundlePackageType
BNDL
CFBundleShortVersionString
1.0
CFBundleSignature
????
CFBundleVersion
1
NSPrincipalClass

```