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: D205 Blank line missing between one-line summary and description
1: D208 Docstring is over-indented
4: I102 copyright year is outdated, expected 2014 but got 2012
31:6: E126 continuation line over-indented for hanging indent
40:6: E126 continuation line over-indented for hanging indent
49:29: E261 at least two spaces before inline comment
54:1: E303 too many blank lines (4)
54: D203 Expected 1 blank line *before* class docstring, found 0
54: D208 Docstring is over-indented
54: D200 One-line docstring should not occupy 3 lines
59:41: E251 unexpected spaces around keyword / parameter equals
59:43: E251 unexpected spaces around keyword / parameter equals
59:66: E251 unexpected spaces around keyword / parameter equals
59:68: E251 unexpected spaces around keyword / parameter equals
59:94: E251 unexpected spaces around keyword / parameter equals
59:96: E251 unexpected spaces around keyword / parameter equals
59:123: E251 unexpected spaces around keyword / parameter equals
59:125: E251 unexpected spaces around keyword / parameter equals
59: D102 Docstring missing
62:49: E127 continuation line over-indented for visual indent
63:49: E127 continuation line over-indented for visual indent
64:49: E127 continuation line over-indented for visual indent
66: D401 First line should be imperative: 'Allow', not 'Allows'
66: D400 First line should end with '.', not 'g'
70: D400 First line should end with '.', not 'r'
75:5: E303 too many blank lines (2)
75: D401 First line should be imperative: 'Return', not 'Returns'
75: D400 First line should end with '.', not 'y'
75: D205 Blank line missing between one-line summary and description
75: D208 Docstring is over-indented
103:28: E713 test for membership should be 'not in'
160:66: E261 at least two spaces before inline comment
187:5: E303 too many blank lines (2)
187: D102 Docstring missing
191:5: E303 too many blank lines (2)
191: D102 Docstring missing
194: D102 Docstring missing
198: D401 First line should be imperative: 'Return', not 'Returns'
198: D400 First line should end with '.', not 's'
198: D205 Blank line missing between one-line summary and description
226: D401 First line should be imperative: 'Find', not 'Finds'
226: D400 First line should end with '.', not 't'
226: D205 Blank line missing between one-line summary and description