Remove the "Rows per page" selector from all data tables

[fabd]

In order to simplify the mobile / desktop layouts and make the UI cleaner, I suggest to remove the "10/20/50" row selectors entirely.

Instead we can settle on a sensible default. In fact the higher the default the less paging and return trips to the server!

Suggested value : 30 rows per page. (easily changed later based on feedback)

Breakdown

• [ ] Create a constant, keep it in the data table component (no need to add a setting to the global configuration files for this)
• [ ] Remove this component from the data table php template
• [ ] Remove the code related to storing / restoring the rows-per-page setting in the user session, and use the constant value instead

[shintoo]

Whenever this update is made, would it be possible to retain the rows query parameter in the URL for this page? I do often use a custom value (e.g. rows=500 in the URL) to get a lot of kanji on one page for example. Thanks!