Add optional axes initial value parameter to handle the trigger behavior

[jlack1987]

Potential fix for #155. I think the right way to fix it is to treat the triggers separately from the axes and to put them in different parts of the message, but I understand there's a lot of inertia here and that would cause a big ripple. I simply added an optional vector of doubles that represent initial axis values on startup.

[JWhitleyWork]

CI passing depends on #218

[peci1]

I think this is not needed. The issue this PR tries to fix has already been fixed in #98 resp. #107. There is an already closed issue on this topic: #91.

The fix is, however, not enabled by default. To make use of it, set default_trig_val to true for joy_node.