Finding a specific F-Curve is often needed in Python, and usually
consists of a construct like:
```
[fcurve
for fcurve in ob.animation_data.action.fcurves
if fcurve.data_path == "location"][1]
```
This can now be written as
`ob.animation_data.action.fcurves.find('location', 1)`
This new function `Action.fcurves.find()` is still O(N) in the number
of FCurves in the Action, but at least it allows us to remove
boiler-plate code. It is also faster than the Python equivalent, as
only the found F-Curve is converted to Python.
Reviewers: campbellbarton, aligorith
Reviewed By: aligorith
Differential Revision: https://developer.blender.org/D1427
89e5c75666