* updated text-filter, fixes LP: #353398
* revert commit 267, a dedicated env-var for indicating a non-composited desktop under UNR is not needed
* revert commit 266, fixes LP: #354349
* don't do any filtering on the summary-text, removed the filter for the summary-text completely
* only pass message-body text through HTML- and markup-filter, the summary text should only be filtered for pango-markup, treat bubble and fallback-dialog in the same manner