WebSubmit: autocompeltion for authors

* Provides an author autocompletion facility for WebSubmit. (closes #2276)

* The author autocompletion interface can easily be configured for each
  submission.

* Author sources can be defined as plugins that return results in JSON.

* Author submission and modification are fully compatible with existing
  BibConvert templates.

* Uses typeahead.js <http://twitter.github.io/typeahead.js/>
  for autocompletion.

Co-authored-by: Harris Tzovanakis <charalampos.tzovanakis@cern.ch>
Co-authored-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
Signed-off-by: Nikolaos Kasioumis <nikolaos.kasioumis@cern.ch>
1: D100 Docstring missing
22:1: F401 'get_dictionary_from_string' imported but unused
32:1: E302 expected 2 blank lines, found 1
32: D103 Docstring missing
41:1: E302 expected 2 blank lines, found 1
41: D401 First line should be imperative: 'Convert', not 'Converts'
41: D202 No blank lines allowed *after* function docstring, found 1
41: D400 First line should end with '.', not 'N'
41: D205 Blank line missing between one-line summary and description
77:33: E126 continuation line over-indented for hanging indent
89:48: E231 missing whitespace after ','
94:43: E231 missing whitespace after ','
94:50: E231 missing whitespace after ','