Issue #134: updated_on column of repositories table required (conservancy/kallithea)

[Michael JasonSmith]

New issue 134: updated_on column of repositories table required
https://bitbucket.org/conservancy/kallithea/issue/134/updated_on-column-of-repositories-table

Michael JasonSmith:

## Currently ##

The *updated_on* column of the *repositories* table is unconstrained. However, if a row has a *updated_on* set to NULL then the repositories page fails to render.

## Expected ##

Either

* The *updated_on* column of the *repositories* table should have a *not null* constraint, or
* Pages that rely on the column should be able to cope with null values.

## Traceback ##

Full traceback in kallithea-last_change-traceback.txt attacked to this issue.

```
#!pytb

File '...kallithea/data/templates/data_table/_dt_elements.html.py', line 400 in render_last_change
  __M_writer(escape(h.age(last_change)))
File '...kallithea/local/lib/python2.7/site-packages/kallithea/lib/helpers.py', line 428 in <lambda>
  age = lambda  x, y=False: _age(x, y)
File '...kallithea/local/lib/python2.7/site-packages/kallithea/lib/utils2.py', line 374 in age
  if prevdate > now:
TypeError: can't compare datetime.datetime to NoneType

```

## Admission ##

I was migrating an old RhodeCode system to Kallithea, so admittedly my data is a little odd, which is why I ran into this issue. However, a vanilla Kallithea 0.2.1 install has the identical problematic schema for the *repositories* table:

```
#!

 created_on       | timestamp without time zone | 
 updated_on       | timestamp without time zone | 

```

My hack around the issue was to add *updated_on* data:


```
#!sql

update repositories 
  set updated_on = created_on
  where updated_on is null;

```