abrt-action-ureport: rewrite in python, improve messages

1. Before this change, "abrt-cli report DIR", if it found that
it was already reported, was saying:
    ABRT Server: URL=https://retrace.fedoraproject.org/faf/reports/8739/
    Bugzilla: URL=https://bugzilla.redhat.com/show_bug.cgi?id=688129
This change makes it:
    A bug was already filed about this problem:
    ABRT Server: URL=https://retrace.fedoraproject.org/faf/reports/8739/
    Bugzilla: URL=https://bugzilla.redhat.com/show_bug.cgi?id=688129

2. If "abrt-cli report DIR" found that ureport was sent, but no bugs were filed,
abrt-action-ureport used to die silently. Now it prints one line:
"uReport was already sent, not sending it again".

3. Since now abrt-action-generate-core-backtrace emits its own message,
"Generating core_backtarce" message at verbosity 1 is removed from here.

To support i18n, the script had to be rewritten in python

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Richard Marko <rmarko@redhat.com>