improve OrderUseStatementsFixer parsing logic

|Q            |A   |
|---          |--- |
|Bug Fix?     |yes |
|New Feature? |n   |
|BC Breaks?   |n   |
|Deprecations?|n   |
|Tests Pass?  |yes |
|Fixed Tickets|#499|
|License      |MIT |

- Sort only the actual namespaces and not complete lines
- Detect traits correctly
- Preserve original white space

Todo:

- [x] Resolve Tokens cache bug
- [x] Add some tests with multiple namespaces 
- [x] Fix comments being moved to the wrong position
                    
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I know but array_merge() reorganizes the array keys :(
 
`Values in the input array with numeric keys will be renumbered with incrementing keys starting from zero in the result array.`

http://php.net/array_merge
http://php.net/array_merge#92602