of one of the axes is a many2one field

[ADD] show grand total
[IMP] classify floats as floats

[IMP] write formatted value to back to input

[RFR] and being on it, make reacting to changes in overrides simple

this is necessary for correct operation after creating new records

* README update to newest OCA template
* Example in README
* Massive performance boost for big matrices, specially on Firefox
* Assign id on row in order to find it back in all cases
* Fix OCA#321, choked on cached writes

Declare as many options prefixed with this string as you need for binding
a field value with an HTML node attribute (disabled, class, style...)
called as the `<name>` passed in the option.

NOTE: This doesn't prevent to require to fill the full matrix with
all the combination records.

…s_clickable attrs

XML attributes for the widget that allows to configure if the axis will be clickable
or not in case the source field is a many2one field.