Make 'extra' data available to other modules

[Alex-developer]

Currently its not easy for modules to read data generated by other modules. Add a function to the shared module that can read all of the extra data files.

[Alex-developer]

Adds a new function to the shared module get_allsky_variable This takes a single parameter, variable and will attempt to find the variable either in the Allsky environment variables or the extra data files.

If the variable cannot be found then Non is returned

Testing requires attempting to read a variable in a module that was generated by anotehr module i.e.

variable="AS_OWWEATHER"
test = s.get_allsky_variable(variable)
print(f"{variable}={test}")`