Allow site admin to configure the content of the editor's Insert button

The site admin should be able by easy means to configure the list of macros which appear on the Insert button of the editor.
Atlassian customers are from different businesses, so there is most likely no ideal list of macros which could be considered "most popular" and deserve to be included in the insert button. Vice versa, customers may want to exclude those macros which don't make sense in their business.

For example the {code} macro is currently not in the "insert" list, although it makes for us a lot of sense to have it there, while other Atlassian customers do possibly not agree.

Therefore I suggest to Atlassian to provide a simple text file (e.g. a properties file) where the site administrator can configure which macros to include in this button.
This should ideally also allow to add macros supplied by the marketplace.