Refactoring Boogie files (#273)
* refactoring including:
- splitting a few source files to adhere to convention that there is code for a single namespace in a file
- removing copyright in source files
- consistently putting using declarations at the top of the source file before the namespace declaration
- removing unnecessary using declarations
- renaming Basetypes -> BaseTypes and BasetypesTests -> BaseTypesTests
* fixed occurrence of Basetypes in BoogiePL.atg
* ran make just to satisfy the travis rule
* renamed directories
* renamed files
* reverting the change
