Add and delete templates

[James-Crean]

The user should be able to add and delete templates at will. Currently there is no functionality for this and the buttons are disabled.

Adding a new template should open a modal that prompts the user to select a base template and a new name. When they select 'Create', it should create this template on the backend and then open the edit modal.

Delete should follow the same idea as the VariableList. Click a template to highlight it and press delete to remove it. (Though the backend will have to be involved in the case of templates.)