made the text and link for the twitter share dynamic

[jhammond2012]

In this PR, both the link and text are dynamic.

[encody]

Part of the issue is that the Twitter button code actually replaces the HTML in the page with an <iframe>, so the computed properties don't update on page navigation because the target element no longer exists (i.e. it has been replaced with Twitter's custom code). One solution to this problem would be to replace this code with a dynamically re-generated bit of HTML code that we stick into a v-html binding, and then re-run the Twitter button replacer code.

[jhammond2012]

@encody I have updated this to rerender on route change.

[encody]

The Tweet button does not appear when loading the overview page from the landing page.