File API gives timestamp in milliseconds, not seconds, so this converts
it on the client-side and sends it the correct time to the server.

Ref T609

- Changes Import link location in dropdown menu
- Makes design consistent with Invite People page (and extracts some
  common CSS into core.less)
- Selects the user's first blog by default in the dropdown
- Changes the copy a bit

Ref T609

handler for post request to import is now under /api/me/import
form target updated

also allow all plaintext files in form

different template action for partial or complete import success

this adds basic support for importing files as blog posts.

.txt and .md are supported at this time and the
collection is selectable, defaulting to draft.

if a collection is specified the post is federated.