Improve jinja capabilities further

[gilesknap]

A few more improvements to jinja

• object references are now true objects in jinja
• therefore e.g. motors can add to a list set up by their controller
• see https://github.com/epics-containers/ibek/blob/d0fb244a9a4b8492915339b731a2f4993431fce5/tests/samples/support/technosoft.ibek.support.yaml#L213-L217
• the _global.counter feature has been renamed incrementor and always takes a increment value - thus allowing simplification of initialization and update of a variable
• eg. this value that accumulates in powers of 2 https://github.com/epics-containers/ibek/blob/d0fb244a9a4b8492915339b731a2f4993431fce5/tests/samples/support/fastVacuum.ibek.support.yaml#L128-L132
• also counters are included in the global variables and accessible via '_global.get'
• e.g. axisNum here https://github.com/epics-containers/ibek/blob/d0fb244a9a4b8492915339b731a2f4993431fce5/tests/samples/support/technosoft.ibek.support.yaml#L37-L53