TopicsStats library name

[francocipollone]

Context

ign-gui0 provides out of the box a TopicsStats plugin that is used in the visualizer0.
When created, this shared library is called libTopicsStats.so.

For the migration to ign-gui3, a new TopicsStats plugin is created in delphyne_gui because the TopicsStats was discontinued in ignition-gui.
To avoid any kind of conflicts when discovering the plugins(because of an equal name), this shared library is called libTopicsStatsPlugin.so.

Victory Condition

After completing the migration (#332) and removing the ign-gui0 dependency, the name of the library should be changed to:
libTopicsStatsPlugin.so --> libTopicsStats.so.

[francocipollone]

Solved at #401