ISIS-537 Made Edit (OK/Cancel) buttons for EntityPropertiesPanel panel bigger (btn-md) than the other buttons in the page (additional links, btn-sm)

https://trello.com/c/ySlNgRB5/81-nice-easy-one-edit-button-needs-to-be-a-bit-bigger-ok-cancel-for-action-dialog-ditto
ISIS-537 Add configuration settings for enabling the theme chooser (isis.viewer.wicket.themes.showChooser) and for enabling just a subset of the themes (isis.viewer.wicket.themes.enabled)

https://trello.com/c/0D6c2jdc/48-provide-the-ability-to-disable-a-theme-chooser-and-programmatically-configure-the-app-to-run-with-a-specific-theme-estatio-will-