Improve the local filter to refer other tab

Modify the local filter to accept an optional string argument, the tab
name to refer.
Add a special handler for TargetInvocationException in query compiler

Since the message of TargetInvocationException is not meaningful,
unwrap the inner exception and throw it.
Reformat the code
Change the default tab name: it's not empty :)
Add "caseful" operator for case-sensitive querying

Add "caseful" unary operator for string to switch string comparison
mode to case-sensitive (default is case-insensitive).
Fix the behavior of the operator = for strings (it compares
case-sensitively, conflict with other operators).
Fix code formats.
Fix filter key of conversations
Merge pull request #69 from takeshik/improve-query

Improve query