RoboVM for Windows/Linux: toolchain and iOS SDK installer

First POC Linux/Windows build has major usability flaw: to start working on Linux/Windows user had to have access to Mac to obtain Xcode files and also manually download and deploy toolchain files. Now it is solved with automatic downloader/installer:
This became possible with as result of following changes:

• Homemade iOS SDK – no dependency on Apple;
• Enhanced version check;

Beside changes shown in gif above Update Checked was updated to monitor for upcoming updates to toolchain/sdk. As per today these changes are not final and bugs are expected. All changes can be seen in github dkimitsa/robovm repo.