Add README file for `sessions` directory.
On branch master, changes to be committed:
	new file:   config/sessions/README.md
Add initial implementation for a settings editor.
On branch master, changes to be committed:
	modified:   src/Lepton.pro
	modified:   src/mainwindow.cpp
	modified:   src/mainwindow.h
	modified:   src/mainwindow.ui
	new file:   src/settingseditor.cpp
	new file:   src/settingseditor.h
Implement a UI form for the settings editor.
On branch master, changes to be committed:
	modified:   src/Lepton.pro
	modified:   src/settingseditor.cpp
	modified:   src/settingseditor.h
	new file:   src/settingseditor.ui
Add temporary text to settings editor.
On branch master, changes to be committed:
	modified:   src/settingseditor.ui
Correct the order of steps taken for loading sessions.
On branch master, changes to be committed:
	modified:   src/mainwindow.cpp
Change the name of 'Settings' menu.
On branch master, changes to be committed:
	modified:   src/mainwindow.cpp
	modified:   src/mainwindow.ui
Implement actions to let the user switch between tabs and spaces for indents.
On branch master, changes to be committed:
	modified:   src/mainwindow.cpp
	modified:   src/mainwindow.h
	modified:   src/mainwindow.ui
Remove unusable shortcut.
On branch master, changes to be committed:
	modified:   src/mainwindow.ui
Remove unused `Document` menu.
On branch master, changes to be committed:
	modified:   src/mainwindow.ui