Remove index-related stuff
Remove reference to index, change some things to 'position'
Add position column to tasks, which will become unique position index
Make positions column an index
Remove index-related code from task model
Remove index-related code from task model
Remove index-related code from task model
Add acts_as_list gem to help with indexing tasks
Create task list table to use with acts_as_list
Add new task_list model and configure association with tasks
Tweak schema to work with acts_as_list, make some changes to make tests pass
Make changes to incorporate new stuff into tests & make them pass