This could be done by each application, but it does cost only a few
lines of code, and it helps standardizing the Owl ecosystem.
For example, some library (such as o_spreadsheet) needs to mock side
effects, and Odoo also needs to do that, so this prevents duplicated effort.
closes#686
With this commit, we can now decides precisely if a component should be
rerendered, by using a hash function.
By default, the hash function will deep observe each store element
coming from the result of the mapStateToProps.
closes#24
Géry Debongnie