Description:
The document templates are currently organized in categories by the Template Manager (`File > Templates > Manage templates`). The categories are taken from the folders contained in the template paths specified in `Tools > Options > Libreoffice > Paths > Templates`.

Currently only one level of template categories is displayed. Sub-categories are not displayed.

For example: if the template path is set to `TemplateTest/`, the `TemplateTest/categoryA/letter.ott` template is displayed inside the `categoryA`, but the `templatepath/categoryA/subcategoryA/subletter.ott` template is not shown at all, not even in the `categoryA`.

Complex organisations have lots of templates. So it would be **very useful** to have nested categories in the Template Manager, to better classify them (eg. by office and by process).

This is why I suggest:
 * allowing nested template categories, from nested folders in the selected template paths;
 * using a directory-like visualization for categories and sub-categories, instead of the `Category` pop down in the Template Manager, because it seems more friendly to basic office users.

For comparison, this seems already possible in the many Microsoft Office versions, see how it works there: http://www.addbalance.com/usersguide/templates.htm


Steps to Reproduce:
1. Create a new folder `TemplateTest` and add it in `Tools > Options > Libreoffice > Paths > Templates`
2. Create and put a `letter.ott` template into the `TemplateTest` folder.
3. Create a nested folder called `categoryA` inside the `TemplateTest` folder
4. Create and put a `letter2.ott` template into the `categoryA` folder.
5. Create a nested folder called `subcategoryA` inside the `categoryA` folder
6. Create and put a `letter3.ott` template into the `subcategoryA` folder.
7. Open the Template Manager with `File > Templates > Manage templates`
8. The templates `letter.ott` and `letter2.ott` are displayed, `letter2.ott` is not. No sub category is shown as well.


Actual Results:
The templates `letter.ott` and `letter2.ott` are displayed, `letter3.ott` is not. No sub category is shown as well.

Expected Results:
The templates `letter.ott`, `letter2.ott`, and `letter3.ott` should be displayed.
The nested sub category `subcategoryA` should be displayed as a folder of `categoryA`.


Reproducible: Always


User Profile Reset: No



Additional Info:
Thank you!