[uml_view] Investigate high memory consumption of the "uml_view" in case of "too many messages fitting for creation of the sequence diagram"

[svlad-90]

How can one reproduce this issue?

1. Work with the data set that contains ~ 2M messages ( ~ 512 Mb of data )
2. Work with the regular expression that makes it possible to create a sequence diagram out of those 2M messages. The "UML" checkbox in the "Search view" should become available for all the found messages, after the search is started.
3. Start the search
4. Check the memory consumption. It might increase up to > 10 GB

This is a new issue caused by the creation of sequence diagrams for a large number of messages. The plugin was not used in this way before, so it was expected that something like this might happen.

=> It is not a memory leak, but rather a properly allocated, still huge area of memory, that is used for storing the sequence diagram metadata. At least now we have such an assumption, that should be checked.

Use Valgrind massif to locate the high memory consumption location. Then try to eliminate it.