Feature/customization and some bug fixes

[failynsedik]

Added a few more customization of the UI.

This can be used just the same as the other config properties, like so:

let config = BConfiguration.init()

config.chatBgColor = "aeaeae"
config.addShadowToMessageBubble = true
// etc.

BChatSDK.initialize(config, app: application, options: launchOptions)

If the added customizations are not set, then the UI will be just like nothing was added, just the base UI itself.

[failynsedik]

I believe changes starting from commit ff21242 is not necessary, but I am not quite sure. I think the "unrecognized selector" crash is only happening because of an update in the library. For more info, I came to this conclusion because of the following:

https://stackoverflow.com/questions/22932402/unrecognized-selector-sent-to-instance-on-ifbool#comment35019597_22933656

[failynsedik]

Currently separating this pull request into their own branches and pull requests for easier review.