Adding support for strings-rules. Extending IDA plugin functionality

[FlxP0c]

In this Pull Request I:

• Added support for strings in rules
• Extended the IDA plugin by a "String Yara Rule" option
• Added a "clear" button to the IDA plugin windows
• Added support for multiple patterns in one rule for the IDA plugin

Sorry for some larger refactoring. But it was necessary in order to introduce the new features. The support for multiple patterns now also changes the behavior of the IDA plugin a bit, I hope that is ok for you. :)

[jellever]

Thanks for the commits :+1: I will look into your commits suggestions and see if I can merge/incorporate them into mkYARA soon :)