[IMP] uom: measurement type on category

In order to restrict some uom field to some uom category, it is required to
add a measurement type on uom.category. Also, this will lessen the use of
master data.

Some technical justifications:
- measure_type is not required, to allow people creating their own
uom.category. Those ones will not interfere with addons business.
- measure_type is unique: we restrict to only one category containing
time, weight, ... in order to avoid mismatch category during conversion.
(2 different weight categories can not be converted).
- measure_type on uom.uom is stored: to allow search and domain on
field, we need to store it. Usually, UoM are not updated every day,
and the number of uom in a database is not that important.

To illustrate this mecanism, a domain is added on
'project_time_mode_id', in project module. This field
is use as timesheet default uom, and we obviously want to
restrict it to time category (timesheeting in liter does
not make sense ...)

Task #1820076

addons/uom/data/uom_data.xml

@@ -6,18 +6,23 @@
         -->
         <record id="product_uom_categ_unit" model="uom.category">
             <field name="name">Unit</field>
+            <field name="measure_type">unit</field>
         </record>
         <record id="product_uom_categ_kgm" model="uom.category">
             <field name="name">Weight</field>
+            <field name="measure_type">weight</field>
         </record>
         <record id="uom_categ_wtime" model="uom.category">
             <field name="name">Working Time</field>
+            <field name="measure_type">time</field>
         </record>
         <record id="uom_categ_length" model="uom.category">
             <field name="name">Length / Distance</field>
+            <field name="measure_type">length</field>
         </record>
         <record id="product_uom_categ_vol" model="uom.category">
             <field name="name">Volume</field>
+            <field name="measure_type">volume</field>
         </record>
        <!--
             Resource: uom.uom