journal: make "repository:" filtering condition work as expected (Issue #261)

Before this revision, journal filtering conditions like as below never
match against any entry, even if there are corresponded repositories.

- repository:foo/bar
- repository:foo-bar

Whoosh library, which is used to parse filtering condition, does:

- treat almost all non-alphanumeric characters as delimiter at
parsing condition
- join each conditions at filtering by "AND", by default

For example, filtering condition "repository:foo/bar" is translated as
"repository:foo AND repository:bar". This combined condition never
matches against any entry, because it is impossible that "repository"
field in DBMS table "user_logs" has both "foo" and "bar" values at
same time.

Using TEXT for "repository" of JOURNAL_SCHEMA causes this issue,
because TEXT assumes tokenization at parsing.

In addition to it, using TEXT also causes unintentional ignorance of
"stop words" in filtering conditions. For example, "this", "a", "you",
and so on are ignored at parsing, because these are too generic words
(from point of view of generic "text search").

To make "repository:" filtering condition work as expected, this
revision uses ID instead of TEST for "repository" of
JOURNAL_COLUMN. ID avoids both tokenization and removing "stop words".

This replacement should be safe with already existing DBMS instance,
because:

- JOURNAL_SCHEMA is used only to parse filtering condition
- DBMS table "user_logs" itself is defined by UserLog class
(in kallithea/model/db.py)

BTW, using ID also avoids normalization by lowercase-ing. But this
doesn't violate current case-insensitive search policy, because
LOWER-ing in actual SQL query is achieved by get_filterion() or so in
kallithea/controllers/admin/admin.py.