BibIndex: refactoring and author parent tokenizer

* Refactoring of BibIndex:
  implements inveniosoftware#1710

* Adds a generic parent tokenizer, useful for the dataset records:
  implements inveniosoftware#1885

* Adds 4 demo records for testing purpose

* Adds (and fixes) tests

More details:

* Refactoring of `task_run_core` in `bibindex_engine.py`: easier to
  follow, moves the decision of which records need to be reindexed to
  the tokenizers

* Fixes bug: the command `bibindex -w [index name] -m [date range]`
  previously was updating the `last_updated` field of the index

* Moves many of the index specific special cases from
  `bibindex_engine.py` to the tokenizers
  (e.g. `if index_name == "author": # add special tokens`)

* Moves some utility functions from `bibindex_engine.py` to
  `bibindex_engine_utils.py`

* Adds tokenizers `BibIndexAbstractParentTokenizer`,
  `BibIndexCanonicalAuthorTokenizer`,
  `BibIndexExactParentAuthorTokenizer`,
  `BibIndexParentAuthorTokenizer`,
  `BibIndexParentCanonicalAuthorTokenizer`

* Adds indexes `simpleauthor`, `canonicalauthor`, `parentauthor`,
  `parentcanonicalauthor`, `exactsimpleauthor`, `exactparentauthor`

* Adds fields `simpleauthor`, `exactsimpleauthor`

* Adds upgrade script for the database changes
  (uses function upgrade_atlantis)

* Transforms `author` and `exactauthor` indexes from regular to
  virtual index

* Adds file `bibindex_engine_tokenizer_regression_tests.py`

* Adds tests for tokenizers, for bibindex CLI, for bibindex utils

* Closes inveniosoftware#1662
  (BibIndex: --reindex should not zero last_updated)

* Edits the commands run by `--load-demo-records` in order to
  reindex the bibauthorid-dependant indexes after the `bibauthorid`
  task (for example `canonicalauthor` and `parentcanonicalauthor`)
1: D200 One-line docstring should not occupy 3 lines
4: I102 copyright year is outdated, expected 2014 but got 2013
39: D203 Expected 1 blank line *before* class docstring, found 0
39: D400 First line should end with '.', not 't'
39: D200 One-line docstring should not occupy 3 lines
45: D102 Docstring missing
49: D400 First line should end with '.', not 's'
65: D400 First line should end with '.', not 'd'
71: D400 First line should end with '.', not 's'
76: D400 First line should end with '.', not 's'
89:5: E303 too many blank lines (2)
89: D400 First line should end with '.', not 's'
98: D203 Expected 1 blank line *before* class docstring, found 0
98: D400 First line should end with '.', not 't'
98: D200 One-line docstring should not occupy 3 lines
104: D102 Docstring missing
108: D400 First line should end with '.', not 'f'
115: D400 First line should end with '.', not 'd'
119: D400 First line should end with '.', not 'n'
143: D400 First line should end with '.', not 'L'
245: D400 First line should end with '.', not 'n'
258: D203 Expected 1 blank line *before* class docstring, found 0
258: D400 First line should end with '.', not 's'
258: D200 One-line docstring should not occupy 3 lines
264: D102 Docstring missing
268: D400 First line should end with '.', not 's'
280: D203 Expected 1 blank line *before* class docstring, found 0
280: D400 First line should end with '.', not 's'
280: D200 One-line docstring should not occupy 3 lines
286: D102 Docstring missing
290: D400 First line should end with '.', not 'c'
305:1: E302 expected 2 blank lines, found 1
305: D203 Expected 1 blank line *before* class docstring, found 0
305: D400 First line should end with '.', not 'd'
305: D200 One-line docstring should not occupy 3 lines
311: D102 Docstring missing
315: D400 First line should end with '.', not 'd'
321: D400 First line should end with '.', not 'd'
324:143: E502 the backslash is redundant between brackets
325:17: E128 continuation line under-indented for visual indent
330:1: E303 too many blank lines (3)