#122 Set breakpoints on method contracts

[Charles Reis]

Story: User starts the debugger and wants a breakpoint
to be hit any time the foo() method is called. User
right clicks on the method contract of foo() and
selects "Toggle Breakpoint". He then invokes foo()
from the Interactions Pane and the breakpoint is hit.

Notes: Currently, breakpoints can only be set on lines
of executable code. Supporting this will involve
identifying that the caret is on a method contract and
then creating a MethodEntryRequest using JPDA.