Convenient access to commands

[TikhomirovSergey]

Change list

• update to Selenium 2.53.1
• the new class CommandExecutionHelper
• the new class AndroidMobileCommandHelper
• the new class IOSMobileCommandHelper
• MobileCommand.commandRepository is mutable now. Additional commands could be defined via
  MobileCommand.commandRepository.put(String, CommandInfo) there.
• source code reafactoring

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Details

There are projects which based on Appium (modifications, additional customized automation layers and so on). In order to make client convenient these chandes were made:

• the ability to define additional commands directly was provided.
  MobileCommand.commandRepository.put(String, CommandInfo)
• access to mobile OS-specific commands and execution was made easier
• was added the ability to implement specific exctentions of the accessing to additional commands and execition.

[TikhomirovSergey]

@SrinivasanTarget @jlipps @philgreenyouilabs @pfoster-youitv @simongranger
Could you please review this PR?

#429

[SrinivasanTarget]

@TikhomirovSergey Interesting. I like this PR 👍there are some remarks from @codacy-bot. I will review soon.

[pfoster-youitv]

Looks to be about the same as what you showed me on your fork. I took that previous one and made use of it for our You.i Engine side of things and it worked really well.

I liked how I could subclass AppiumDriver and import commands from various devices. This will really make cross platform commands easier to call.

👍 from me

[TikhomirovSergey]

@SrinivasanTarget Issues were fixed. You are free to review it

[SrinivasanTarget]

@TikhomirovSergey LGTM 👍