tahoe.css: fix #section typo, update welcome.xhtml to match

The "#section" declaration (which matches id="section") should have been
".section" (which matches class="section").

The welcome page has a feature that I actually liked: the little "This
Client" sidebar sits just to the right of the start of the Controls block.
Fixing .section broke that (the clear:both introduces a gap, forcing the
Controls block to start strictly below the bottom of the This Client block).
So I also removed class="section" from the Controls block to allow them to
share the horizontal space again.
introducer web page: add CSS styling, roughly match client Welcome page

Also add /static and the top-level /tahoe.css -type stuff to the introducer's
web server.
add some quick tests of the introducer/web improvements
Add nickname/nodeid to storage-status web page. Closes #1204.

Also add tahoe.css to the page, to make it look slightly prettier.
Suppress a warning from win32eventreactor on Windows (patch v2). fixes #1681
Update various references to allmydata.org or http://tahoe-lafs.org in comments, to https://tahoe-lafs.org. refs #1682
Make the link on the Welcome page to 'https://tahoe-lafs.org/', not 'http:'. Includes a test. fixes #1682
Update copyright notices. refs #1686
bump pycryptopp dependency to >=0.6.0, to get ed25519 signatures

This is for the upcoming #466 signed-introducer code.
'tahoe admin generate-keypair/derive-pubkey': add Ed25519 keypair commands

Also add parse_privkey/parse_pubkey tools to util.keyutil
new introducer: signed extensible dictionary-based messages! refs #466

This introduces new client and server halves to the Introducer (renaming the
old one with a _V1 suffix). Both have fallbacks to accomodate talking to a
different version: the publishing client switches on whether the server's
.get_version() advertises V2 support, the server switches on which
subscription method was invoked by the subscribing client.

The V2 protocol sends a three-tuple of (serialized announcement dictionary,
signature, pubkey) for each announcement. The V2 server dispatches messages
to subscribers according to the service-name, and throws errors for invalid
signatures, but does not otherwise examine the messages. The V2 receiver's
subscription callback will receive a (serverid, ann_dict) pair. The
'serverid' will be equal to the pubkey if all of the following are true:

  the originating client is V2, and was told a privkey to use
  the announcement went through a V2 server
  the signature is valid

If not, 'serverid' will be equal to the tubid portion of the announced FURL,
as was the case for V1 receivers.

Servers will create a keypair if one does not exist yet, stored in
private/server.privkey .

The signed announcement dictionary puts the server FURL in a key named
"anonymous-storage-FURL", which anticipates upcoming Accounting-related
changes in the server advertisements. It also provides a key named
"permutation-seed-base32" to tell clients what permutation seed to use. This
is computed at startup, using tubid if there are existing shares, otherwise
the pubkey, to retain share-order compatibility for existing servers.
Update more links from http: to https: in documentation and comments.
Minor updates to URLs.
Update find_links URLs in setup.cfg to https://tahoe-lafs.org. This is not just a doc change; look out for compatibility problems.
minor: hush pyflakes, move pycryptopp dep to unconditional section

Also change Makefile's "pyflakes" rule to emit less output, so buildbot will
count errors properly.
Temporarily suppress the DeprecationWarning about IFinishableConsumer; it's irritating, but not in a way that is likely to make me fix the underlying issue (#1525) any sooner :-). refs #1295
Fix a missing comma in the last patch. refs #1295
IServer.get_name(): remove v0- prefix from displayed server names

Don't remove the prefix if it isn't there: that avoids the need to fix tests
which use a bogus key (usually all-zeros).
Fix mutable status (mapupdate/retrieve/publish) to use serverids, not tubids

This still leaves immutable-publish results incorrectly using tubids instead
of serverids. That will need some more work, since it might change the Helper
interface.
Correct a link to frontends/drop-upload.rst. fixes #1690