As mentioned in commit 925f04e3f, icon classes make screen readers
announce strange symbols and aren't properly displayed for people who
have changed their preferred font family.
This way we simplify the ERB code.
Due to the bug mentioned in the previous commit, we're keeping the
original code instead of using `can?` to check permissions.
We were using similar code in four different places; six, if we count
the welcome pages seeds. Reducing duplication in the pages seeds is a
bit tricky because administrators are supposed to edit their content and
might remove the HTML class we use to define styles. However, we can
share the code everywhere else.
Note that there's a bug in the application since we show that level 2
users cannot vote for budget projects but we give them permission to do
so in the abilities model. We're keeping the same behavior after this
refactoring but we might change it in the future.
