Localize custom procedure modal title

* Added localization for ‘Make a Block’
* ‘block name’ default text is in scratch-blocks

The changes in `error-step.jsx` were needed because the same id was defined in there and `unavailable_step.jsx`. The scripts to generate the json file for Transifex give an error if the same id is defined in two places. In error step it simply uses the id without redefining default value etc. The alternative would be to add a new messages.jsx file that has the definitions for shared text and include that in both places that use them.