Reuse the fields in SourceLineAnnotation class for the bug instance created for keshmesh fixer

[samira-t]

For adding a fixer for LCK02J, we reused some fields in SourceLineAnnotation to fill out the information needed by Keshmesh fixer as following:

• startBytecode and endBytecode (in SourceLineAnnotation) as firstOffset and lastOffset (in Keshmesh BugInstance)
• description (in SourceLineAnnotation) as typeNames (in Keshmesh BugInstance, if typeNames just contain one element. In the case that the typeNames contains more than one element we don't fix that and we set description to null).

We need to find a solution for that. We can add any annotation like (SourecLineAnnotation) to the BugInstance class of Findbugs to fill additional information. But that solution needs changing Findbugs.

[reprogrammer]

Issue #22 computes the offset information in the fixer. So, we no longer need to worry about passing the first and last offsets of the bug instance to the fixer.