Refactor account_asset.py

We are interested in using the asset_management but we need it to be inheritable in order to add information in created moves. I propose to refactor the code of method create_move so it can be extended to add or replace values in move and move_lines objects.

Our final goal is to add analytic distribution in move_lines.

I also fixed an issue where the context was not passed in some methods: instead of creating a new context, update the current context.

PS: Do you know if/when your pull request will be integrated in OCA ?