Replace model symbol hash rockets with 1.9 syntax

A better place to review this PR is at https://github.com/zhangsu/Markus/commit/a54a9e615c18e71ff3c43ae8c2e0d6fcd4e2150d
with no Hound comments since this PR doesn't address style issues.

This is a global search-and-replace that replaces the Ruby 1.8 symbol
key hash rocket syntax to Ruby 1.9 syntax in model code.

Since this is a big change list, the style issues in the changed lines
are not being dealt with so that errors are minimized and code review
is easier. There is one exception though:

If the lines before the change have a good alignment of hash keys that
span multiple lines and the lines after the change do not (because the
change might alters the number of spaces needed for the alignment), then
the alignment is fixed, such that no new style issues are introduced. If
the alignment was not correct to begin with, then it is not fixed.

As a result, please ignore linter comments for this change.

This is for #1498.

Tested:
- rake test:units
- rake test:functionals
- rails s