Implement sending stickers

MSC2545 image packs are used as source. Currently, only room image pack
events are supported.
3 jobs for !321 with work/sendstickers in 1 minute and 20 seconds (queued for 19 seconds)
latest merge request
Name Stage Failure
failed
suse_tumbleweed_qt515 Build
ERROR: No files to upload                          
Uploading artifacts...
WARNING: CoberturaLcovResults.xml: no matching files
ERROR: No files to upload
Uploading artifacts...
WARNING: cppcheck.json: no matching files
ERROR: No files to upload
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1

failed
android_qt515 Build
                                                                                               ~~~~~~~~ ^  ~~~~~
1 warning and 3 errors generated.
make[2]: *** [src/CMakeFiles/neochat.dir/build.make:655: src/CMakeFiles/neochat.dir/imagepacksmodel.cpp.o] Error 1
2 warnings generated.
make[1]: *** [CMakeFiles/Makefile2:254: src/CMakeFiles/neochat.dir/all] Error 2
make: *** [Makefile:160: all] Error 2
## Failed to build the project
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1