ios: API: rename 'getter' for 'modules'

Inside of the following classes we have a getter, to get an actual object by its name:

• AGPipeline
• AGDataManager
• AGAuthenticator

However, this is not best practice. Usually a method that starts with 'get' deliver values by reference

See NSColor (https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ApplicationKit/Classes/NSColor_Class/Reference/Reference.html)

- (void)getComponents:(CGFloat *)components

Instead of, for instance:

- (id<AGAuthenticationModule>)get:(NSString *)moduleName

we can have something LIKE this:

- (id<AGAuthenticationModule>)loadModuleNamed:(NSString *)moduleName

Current 'get' methods:

• https://github.com/aerogear/aerogear-ios/blob/master/AeroGear-iOS/AeroGear-iOS/pipeline/AGPipeline.h#L88
• https://github.com/aerogear/aerogear-ios/blob/master/AeroGear-iOS/AeroGear-iOS/datamanager/AGDataManager.h#L62
• https://github.com/aerogear/aerogear-ios/blob/master/AeroGear-iOS/AeroGear-iOS/security/AGAuthenticator.h#L62