Updating packages to 0.20.0-rc.1-1

Changing the release number of graylog2-server.spec and
graylog2-web-interface.spec to rc.1-1 and adding a changelog entry
for the new release.

Not 100% sure if an RPM build will work since the relase number
now contains a dash. May result in a custom build specific only
to this release.
Reverting the release number back to rc.1

Since the rc.1-1 release is a special case because of the dash
in the release number a standard increment in the release number
in SPECS/graylog2-server.spec and SPECS/graylog2-web-interface.spec
cannot be completed. The RPM builds fail because of illegal char
'-'.

In both files, resetting the Release number, removing the changelog
entry and updating the Source0 and setup entries.
Replacing all string matching the package name with the name setting.

In graylog2-server.spec all matching "graylog2-server" strings, in
the Sources list and install step are replaced with %{name}.

Same in graylog2-web-interface.spec with "graylog2-web-interface"

The spec files are as a result smaller and more portable. Allowing
for another related package, for instance graylog2-radio, to be
created as a copy if an existing spec. Fewer changes will have
to be made as a result.