Updater (Swing): remove the 'For upload' checkbox in the sites dialog

We want to actively blur the lines between developers and users,
especially now that we offer personal update sites to offer macros
and plugins. So it does not make sense to make it too hard to add
upload sites...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater: stop warning about update sites shadowing others

We want to allow overriding (shadowing) other update sites' files. So
do not scare users who do that. Or for that matter, do not scare users
of Fiji (that does shadow a couple of files from ImageJ's update site).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater's 'Manage Update Sites' (Swing): make the table editable

... instead of opening yet another dialog.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater's 'Manage Update Sites' (Swing): remove the 'Edit' button

... because it is obsolete now.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater (Swing) Proxy Authenticator: fix 0-width input fields

This fixes part of ticket 1875.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater (Swing) Authenticator: it handles more than proxy
authentication

The Authenticator handles all kinds of authentication. Tell the user
what requests authentication this time.

This fixes another part of ticket 1875.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
WebDAV uploader: handle incorrect passwords more gracefully

The directoryExists() method really wants to let us know when the
credentials were incorrect. Let it do so.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater: Fix a NullPointerException

Local-only files can have update site values 'null'. So let's be very
careful when we rename update sites.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater (Swing): allow Unicode passwords

Internally, Java still uses ISO-8859-1 which -- if you think long and
hard about it -- might have been slightly shortsighted, but at least
one can understand that if English was good enough for Jesus, it is
good enough for any programming language. The only funny thing there
is that even variable names in Java can contain umlauts. But I digress.

As mentioned above, internally, Java still uses ISO-8859-1 and while
the authenticator purports to work on char arrays for passwords
instead of byte arrays, internally it simply casts chars to bytes,
in effect handling char arrays as if they were raw bytes:

http://hg.openjdk.java.net/jdk7/jdk7/jdk/file/96c75aec5545/src/share/classes/sun/net/www/protocol/http/BasicAuthentication.java

So while it would be awesome to work with properly encoded Strings
all the time, we cannot... Let's work around this issue by treating
the password as the UTF-8-encoded String it should have been.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
WebDAV uploader: handle Unicode passwords

It's easier here than with the SwingAuthenticator because we do
not have to rely on Java's runtime libraries to do the right thing
regarding encodings.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>