Accept UIAppearance

Added capacity to customize layout using UIAppearance
Now you have one alternative to customize TSMessageView, you can use UIAppearance.
These are the properties 
```objective-c
[TSMessageView appearance] setTitleFont:[UIFont boldSystemFontOfSize:6]];
[[TSMessageView appearance] setTitleTextColor:[UIColor redColor]];
[[TSMessageView appearance] setContentFont:[UIFont boldSystemFontOfSize:10]];
[[TSMessageView appearance]setContentTextColor:[UIColor greenColor]];
[[TSMessageView appearance]setErrorIcon:[UIImage imageNamed:@"NotificationButtonBackground"]];
[[TSMessageView appearance]setSuccessIcon:[UIImage imageNamed:@"NotificationButtonBackground"]];
[[TSMessageView appearance]setMessageIcon:[UIImage imageNamed:@"NotificationButtonBackground"]];
[[TSMessageView appearance]setWarningIcon:[UIImage imageNamed:@"NotificationButtonBackground"]];
```