LocationAlias now keeps track of the original location.

The LocationAlias table mapped names to Locations. When a checklist
was loaded the Location was selected by first checking the LocationAlias
table and assigning the associated Location if an entry matching the
name in the checklist JSON data was found. This destroyed information
in that it was not possible to infer the original location if more than
one entry in the LocationAlias table mapped to a given Location. It also
meant that when a checklist was loaded if the alias was used then it was
not possible to update the location coordinates for example so the
information in the database was out of sync from the information in
the database from which the checklist was downloaded.

The name field was replaced by another foreign key to Location. Now
a checklists Location is only updated in the admin, not when the
checklist is loaded. That still does not solve the problem of tracking
the original location, though this can be done through the URL to the
checklist in the original database. However the Location objects which
were created from the data in the JSON checklist can now track the
values from the remote database.
Replaced taggit tag fields with specific purpose status tables.

The general purpose tag system using django-taggit was dropped and
replaced by tables used specifically for recording status information.
For Species, SpeciesStatus will contain keywords describing the
occurrence of a species in the geographical area covered by a given
database. For Entries, EntryStatus will contain keywords describing
the signficance of a given record. The tags for Location and Checklist
were not replaced by anything, for now.
Tidied up generating fieldnames in list_display, search_fields, etc.

Fields which are internationalized using Transmeta must have all the
different language variations listed explicitly in ModelAdmin fields
such as list_display, search_fields etc. Previous a single function
was used to generate the list for all the fieldnames at once. This
was simplified so there is a separate function call for each name
which is neater and a lot easier to read.
Tidied up admin, factoring out forms and utility functions.

Also replaced the ModelLinkWidget which was used to add and edit line
to the EntryInLine with a simpler, read-only field.
PEP8 cleanup