Currently in search dialog (or gadgets in new UI) the functions for comparison are a bit hard to understand for the users. For example, user sees "Not Greater Than", which in reality means "Less Or Equal To" (the "or equal" cannot be guessed).

This MR proposes to improve this use case of the ERP5 UI for users, by using better function names, and improving translation if needed.

Also, the functions which were used (min, max, ngt, nlt) can appear in the UI (ie in the input field on each columns of listboxes). This MR also replaces them by their mathematical equivalent, which is in general taught to users (>, >=, <, <=).