Adding a new ACL rule 'core.options'

### Issue
As explained in issue https://github.com/joomla/joomla-cms/issues/4954, currently it's not possible to give someone access to the options without giving him also access to the permissions. It means that a user with access to the options is a "SuperUser" for that particular extension.
There may be use cases where you want to give someone access to the options without giving him full permissions for the extension.

### Solution
This PR adds a new ACL rule `core.options` which will allow to edit the options, but not the permissions.
I only did it for com_content so far, but if the concept is accepted I can easily add it to the other extensions as well. It's just an added line in the access.xml file and an added ACL check in each view where the options button should appear.

### Testing
* Create a second user and adjust the permissions in com_content so he can access the options but doesn't have "Configure" permissions. 
* Check with SuperUser and this new user if the options work as expected. SuperUser should be able to save the permissions. The new user should not see them and not be able to save them (even if he fakes the form).
* Check also in other extensions that the SuperUser still can access and save the options and permissions. Nothing should have changed there.