In Debugger mode watch files and refresh when they change

[hatton]

This change is 

[JohnThomson]

LGTM. Some very minor suggestions, or you can just merge.

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: all files reviewed, 3 unresolved discussions (waiting on @hatton)

---

src/BloomExe/Edit/EditingModel.cs line 1783 at r1 (raw file):

                    if (CurrentBook == null)
                        return;
                    // if we've been called already in the past 5 seconds, don't do it again

2 seconds :-)

---

src/BloomExe/Edit/EditingModel.cs line 1798 at r1 (raw file):

                    // Enhance: I suspect all the problems here are related to us changing the page id's each time we load, which I don't understand.
                    // It may just be a mistake.
                    if (args.Name.EndsWith(".json"))

.ToLowerCaseInvariant() ?

---

src/BloomExe/web/controllers/BrandingSettings.cs line 180 at r1 (raw file):

                    {
                        NonFatalProblem.Report(
                            ModalIf.Beta,

Do we want Alpha, or even do this at all only for developers? At least the message about watch:branding:files will only help devs.