v2.7.12

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