Patch notes:

Changes/bugfixes visible to users:

• index.html now always gets regenerated at the end of running a decker command
• Multiple Choice questions now have a solution button. Also bug fixes with MC
• Writing date: today in Meta files or header writes the current date to the title slide

Internal changes:

• Internal refactoring (no changes visible to outside world)
• Updated node-sass version to 4.12.0 due to incompatibility of version 4.9.3 with Node 12