WebSearch: new service JournalHintService

* Adds the search service JournalHint, that displays "Were you looking for a journal reference? Try: [link]" when the user search for a raw journal reference.
* Adds regression tests to WebSearchServicesJournalHintService.
* Uses refextract to detect if the query is a raw journal reference

Signed-off-by: Federico Poli <federico.poli@cern.ch>
48: D400 First line should end with '.', not 's'
52: D202 No blank lines allowed *after* method docstring, found 1
52: D400 First line should end with '.', not 's'
85: D400 First line should end with '.', not 's'
94:16: E713 test for membership should be 'not in'
102: D400 First line should end with '.', not 's'
118: D400 First line should end with '.', not 'n'
122: D400 First line should end with '.', not 'n'
132: D400 First line should end with '.', not 'e'
145: D400 First line should end with '.', not 'e'
158: D400 First line should end with '.', not 'e'
171: D400 First line should end with '.', not 'e'
179: D400 First line should end with '.', not 'e'
191: D400 First line should end with '.', not 'e'
202: D400 First line should end with '.', not 'n'
206: D400 First line should end with '.', not 'n'
216: D400 First line should end with '.', not 'e'
229: D400 First line should end with '.', not 'e'
242: D400 First line should end with '.', not 'e'
255: D400 First line should end with '.', not 'e'
268: D400 First line should end with '.', not 'e'
278: D400 First line should end with '.', not 'e'
290: D400 First line should end with '.', not 'e'
302: D400 First line should end with '.', not 'e'
312:1: E302 expected 2 blank lines, found 1
312: D203 Expected 1 blank line *before* class docstring, found 0
312: D400 First line should end with '.', not 'n'
315: D400 First line should end with '.', not 'n'
322: D400 First line should end with '.', not 'e'
333: D400 First line should end with '.', not 'e'
344: D400 First line should end with '.', not 'e'
355: D400 First line should end with '.', not 'e'
366: D400 First line should end with '.', not 'e'
377: D400 First line should end with '.', not 'e'
388: D400 First line should end with '.', not 'e'
399: D400 First line should end with '.', not 'e'
410: D400 First line should end with '.', not 'e'
418:36: E225 missing whitespace around operator
421: D400 First line should end with '.', not 'e'
429:36: E225 missing whitespace around operator
432: D400 First line should end with '.', not 'e'
440:36: E225 missing whitespace around operator
443: D302 Use u""" for docstrings with Unicode
443: D400 First line should end with '.', not 'e'
454: D302 Use u""" for docstrings with Unicode
454: D400 First line should end with '.', not 'e'