Feature: Add environment variable Sortby default

[MarcS1975]

Similar to FLATNOTES_QUICK_ACCESS_SORT have FLATNOTES_ALLNOTES_SORT

Reason: Currently the Allnotes list always shows "by Titel". This is the least intuitive sorting method because Flatnotes search is very good anyway. What would be much more helpful in this list is to have default set to Last Modified or as a variable in Docker,

P.S. Actually when clicking the "..." on bottom of Qick Access List, the Allnotes list does default to "Last Modified", just not when Allnotes is selected via the menu.