Update the Terra wdio tree model instead of rebuilding the whole during event processing

[picimako]

Summary of scope

Currently the TerraWdioTreeModel is rebuilt every time a file system change happens inside the wdio test folder. This was a conscious decision as it was easier to implement it, however a updating only parts of the model would probably increase performance, maybe reduce memory consumption of the tool window.

Solution details

• Add functionality to TerraWdioTreeNode implementations to update and query their underlying structures.
• Add logic to TerraWdioTreeModel to update the underlying model objects.
• Dispose logic might need to be updated too, since the model will be created only once.

Out of scope

• N/A

[picimako]

Will not be implemented.