Add joint state publisher and periodic polling

[thettasch]

Added two complementary features to code:

Periodic Polling

Allows for the ACF telemetry to be published at a fixed frequency without requiring constant publishing on /ACF/force. Can be deactivated (by setting the frequency parameter to zero) to yield the old behavior.

Joint State Publisher

The latest position of the ACF can be published as a joint state, for simple integration with robot state publishers. This feature is best used in conjunction with periodic polling to give frequent joint state updates.

Reverse compatibility

When running the package without setting the new parameters (frequency and joint_name), behaviour is unaltered from before.

Tested and works on an ACF/111/04.

[gavanderhoorn]

There is no way to get the ACF itself to periodically broadcast its state?

Polling is typically expensive, so is best avoided if possible.

[gavanderhoorn]

Some comments.

[thettasch]

There is no way to get the ACF itself to periodically broadcast its state?

Polling is typically expensive, so is best avoided if possible.

For the TCP/IP Ethernet interface we're using, unfortunately the ACF only sends force/position information after receiving a command. Thus the necessity for polling to get frequent position updates.

[thettasch]

Finished reviewing comments, have incorporated improvements/modifications where appropriate. Still need to test the modified code on the physical ACF.

[thettasch]

Tested on physical ACF, all appears to be working. Decided to move all topics/services to private naming (except for joint_states).

[thettasch]

@Pugens This should now be ready to merge, unless there are any other minor changes to be made. We can handle the other issues/major changes in future PRs.

[gavanderhoorn]

Friendly ping @Pugens.

[Pugens]

Went through the code comments and fixes again. Everything looks good, merging now