Debugger changes for expression evaluator

ScalaDebugger now capture frame indexes. Frame indexes are needed
to evaluate expressions on stack frames differrent than current one.

Correct SuspendPolicy handling. Before, debugger always suspended thread,
now suspending whole VM is correclty handled.

DebugTarget now stores classpath of underlying project, which is used to
load files to inspect for generics, imports etc.

Minor corrections to ScalaClassFile.
Rest, to be splitted further