Release 1.6

Improvements

• Added a "Convert URL" button. When pressed, SLR will evaluate a normal URL and replace each string of one or more numerals with an equivalent sequence definition, which the user can then edit.
• The location of the application window and the current Options settings are now saved in an "slr.json" file in the application's home directory on Exit, and are loaded upon Startup.
• Updated screenshots and README.md file to reflect the above