Currently the viewer uses semi-private `EventBus.prototype.{_on, _off}` methods, to try and ensure that all internal viewer state is updated *before* any "external" listeners are invoked.
For all use-cases outside of the viewer, e.g in the integration-tests, the `EventBus.prototype.{on, off}` methods are supposed to be used instead.
Unfortunately this isn't currently enforced in any way, except (hopefully) during review, and generally speaking it's not really possible to prevent the semi-private methods being used (e.g. by third-party users).
Hence this patch adds a new `INTERNAL_EVT` property which is *not* exposed anywhere (neither in the API nor globally), and whose value is generated at build-time, that the viewer uses to mark its `EventBus` listeners are internal.
This allows us to remove the semi-private `EventBus` methods, which helps to simplify that class a little bit.
Many `parseInt` call-sites already provide the `radix` argument, and this rule helps improve consistency in the code-base; see https://eslint.org/docs/latest/rules/radix
*Please note:* The rule is disabled in `src/scripting_api/util.js` for now, since it's not obvious at a glance (at least to me) what the correct `radix` argument should be there.
- Point the `addSignatureDescription` respectively `editSignatureDescription` labels to their actual `input`-elements (this way clicking the label will actually focus the input).
- Add the event listener to the `addSignatureDescription`-input, rather than its `span`-element (this is consistent with the `editSignatureDescription` case).
- Correctly check if the `addSignatureDescription`-input is empty, since we're accidentally comparing with its `span`-element.
- Remove unbalanced, and likely accidentally added, `</span>` tags.
It's now pretty common that we only want to close a `dialog` *if* it's currently active, to avoid throwing errors, and this new method provides a shorter and more convenient way to achieve that.
