(core): name convention for the Activities

Description

Currently there is no naming convention for the Activities.

We can find names like:

<id>2DVisualization</id>
<id>3DVisualization</id>
<id>VolumeRendering</id>
<id>SeshatActivity</id>
<id>Processing</id>
<id>DicomFiltering</id>
<id>mesherActivity</id>

CamelCase or not ? Activity at the end or not ?

Proposal

Personally I would say CamelCaseActivity