Make datatable responsive

[JustCarmen]

Added <div class="table-responsive"> around the datatable to allow horizontal scrolling on smaller screens. Otherwise the update button cannot be reached on smaller screens.

[Jefferson49]

Hi Carmen,

thank you very much for providing the pull request. I like the idea of making the table responsive.

However, in tests with the responsive table, it seems to look worse in a normal large screen browser. I tested with Edge and Firefox. In my tests, the right column is "cut off". It seems that the responsive table is rendered differently by webtrees:

The shown issue about the table width and the columns can be improved with the "Configure columns" option offered by the additional button. If some columns are de-selected, the responsive table looks fine again.

Since the responsive table seems to have advantages and disadvantages: What do think about an option to configure the responsive table in the control panel?

General comment: The column width of the table is at its limit anyway. For some users with different browsers, even the current table (non responsive) has columns, which are not visible. Therefore, table and column width is a limited resource.