Add date missing message to InboxToadlet if needed

This adds "Date missing" (or translation) in place of the date if the
message doesn't have a date header (or has one we can't parse). This
avoids leaving the field empty, and is consistent with the handling of
messages without a subject.

Fixes bug 6173
Add date to message view

This adds the message date to the list of headers in the message view,
or a message similar to the one in the folder view if the message
doesn't have a date.

Fixes bug 5836
Rewrite welcome message slightly

A few people have emailed me asking why they have to activate their
account by replying to the welcome message. This changes the welcome
message slightly in order to avoid giving people that impression.

Fixes bug 5923
Fix NPE when displaying a message without a from header

This fixes the message view so a message without a from header doesn't
cause a NPE to be thrown.

Fixes bug 6171
Don't show deleted messages in folder view

This makes InboxToadlet skip deleted messages when displaying the
message list.

Fixes bug 6170
Add from missing message to InboxToadlet if needed

Shows "Sender missing" or equivalent instead of an empty box when a
message is missing the from header.

Fixes bug 6172
Merge remote-tracking branch 'zidel/bugfixes'
Update translations

Thanks to volunteers on Transifex.
Initialize RNG before running message transport test
Mock Executor to fix ordering during transport test

Due to the way operations happen when sending a message a five minute delay
usually occurs when the RTS keys need to be generated. This change mocks the
executor that runs the tasks, and ignores the retry delay when running the
message handler test so it will complete in a reasonable amount of time.
smtp: reject auth when usernames are not the same

The plain SASL authentication mechanism supports a separation between the
authenticating and authorizing users, but Freemail doesn't so reject all
attempts where the two are different.
smtp: don't try to deal with auth plain with one nul

Passing only a single NUL byte in the argument to auth plain is not allowed, so
simplify the code by rejecting it.
smtp: add support for auth cancelation
Don't close test side of the fake socket on close()

Closing the test side of the socket makes it impossible to get the data writen
by the code under test before closing the socket.
imap: fix reading of literals during append

This makes append work for data that doesn't end with \r\n, and might also fix
corruption of lines ending with either \r or \n only.
smtp: reject auth when already authenticated
imap: reject search with extra spaces near paranthesis
Fix EmailAddress test to allow UTF-8
Don't generate .jar unless unit tests pass

Fixes bug 6233
Remove extensive test parameter