Declare dependency on jquery_ui in composer.json

Problem/Motivation

tocify 3.1.x declares a dependency on jquery_ui in its info file, but this is not declared in its Composer file. This makes the module hard to install.

Proposed resolution

Declare the dependency in Composer or remove it from info.

Remaining tasks

Implement.

User interface changes

None.

API changes

None.

Data model changes

None.