Fix: Conditionally strip-out markdown in note previews

[dmsnell]

Tests have been failing because noteTitleAndPreview is reported to be taking
longer than 1ms to run. In fact, Date.now(), which we were using to validate
this, includes reduced time precision for protection against timing attacks. In
this patch I've done two things to address the failing tests:

• Replace Date.now() with process.hrtime() which gives us nanosecond
  precision
• Run the function-under-test 100 times in order to eliminate variance in the
  measurement

While fixing this test I noted a flaw in noteTitleAndPreview that we missed
in #1647. We created the helper function removeMarkdownFromOutput which
transforms a string based on whether or not markdown is enabled for the note.
Unfortunately for us we were setting a module-global function based on the
module-init-time value isMarkdown, which as a function is always truthy,
meaning that it would return a function that alwasy removed markdown regardless
of the note.

In this patch I've addressed this by passing stripMarkdown into that
function. In the PR for #1647 we discussed this parameter and removed it but we
kept removeMarkdownFromOutput outside the scope of noteTitleAndPreview. We
could leave out the parameter and move the function into noteTitleAndPreview
or we could add the parameter back.

For the purpose of only creating that function once I have added the parameter
back in. noteTitleAndPreview gets called in some inner loops and I preferred
to avoid recreating the filtering function on every call, or at least until the
JIT figured it out; I'm sure that the performance impact is insignificant but I
don't see any benefit to one way over the other and I'd rather do less work as
the default.

Sorry @belcherj for not catching this in the original PR

Testing

The test-fix will run itself in CircleCI. You can validate the note list behavior for
notes with and without markdown formatting enabled.

In the following screenshots the notes have the following content:

# Not Markdown

and

# Markdown

Before

After

[codebykat]

Tested this. I noticed that if you change a note from Markdown to non-Markdown, you have to reload before the difference is reflected in the notes list. Is that intentional?

[dmsnell]

Is that intentional?

No but probably related to our odd data flows. Unlikely related to this PR in my guess - I don't know how to confirm that since this behavior was always stripping away markdown before.