Autogenerate proposition voting ID

[dpausp]

It should be possible to autogenerate proposition voting IDs when propositions are assigned to a voting phase from a string template. This is configured per proposition type and is optional.

Example: If the proposition is the first one of its type associated with a voting phase and the string template for the proposition type is "{abbreviation}{:03d}" with abbreviation set to "WP" the voting ID would be "WP001".

[GamesGamble]

this fixes the creating of propositions inside the admin cp with the finished status

[Plexar]

The implementation for issue #11 is suggested as follows by Tobias and Holger:

Counters are managed for each combination of proposition type and voting phase.
A new table named 'voting_id_counter' is created with 3 columns to store these counters:

1. propositiontype_id : id of corresponding proposition type
2. voting phase_id : id of corresponding voting phase
3. counter : counter for this combination

When editing proposition types it is possible to enter a pattern for a proposition
identifier. This pattern can be used for formatting Python strings without prior
processing the pattern. The pattern is stored in the column 'abbreviation' of table
'proposition_types'.

When submitting an edited ballot, the pattern mentioned above is evaluated and the counter
from table 'voting_id_counter' for this proposition type and this voting phase is used to
create new identifiers for the propositions of this ballot. For each proposition the
corresponding generated identifier is stored in column 'voting_identifier' of table
'propositions'. A new identifier for a proposition is generated only if it not yet has
one.

[dpausp]

The pattern is stored in the column 'abbreviation' of table 'proposition_types'.

abbreviation is already present and should be kept. Use a new column voting_identifier_template, for example.