Hash passwords with BCrypt instead of SHA1

BCrypt is regarded as a more secure alternative to hashing using message
digest algorithms, such as MD5 and SHA families [0, 1, 2]. Apart from
built-in salting it is adaptable to the increasing power of modern
processing units, which makes it more secure against brute-force cracking.

This commit makes all passwords hashed using BCrypt. The session tokens
remain generated using SHA1. Tests were updated, `rake test:units` and
`rake test:functionals` didn't report any regressions.

[0] http://bcrypt.sourceforge.net/
[1] http://en.wikipedia.org/w/index.php?title=Bcrypt&oldid=439692871
[2] eab1c72/README.md

spec/fixtures/users.yml

@@ -1,7 +1,7 @@
 # Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html
 admin_user:
   login: admin
-  crypted_password: <%= Digest::SHA1.hexdigest("#{Tracks::Config.salt}--abracadabra--") %>
+  crypted_password: <%= BCrypt::Password.create("#{Tracks::Config.salt}--abracadabra--").to_s %>
   token: <%= Digest::SHA1.hexdigest("adminSat Feb 25 17:14:00 GMT 20060.236961325863376") %>
   is_admin: true
   first_name: Admin
@@ -10,7 +10,7 @@ admin_user:
 
 other_user:
   login: jane
-  crypted_password: <%= Digest::SHA1.hexdigest("#{Tracks::Config.salt}--sesame--") %>
+  crypted_password: <%= BCrypt::Password.create("#{Tracks::Config.salt}--sesame--").to_s %>
   token: <%= Digest::SHA1.hexdigest("janeSun Feb 19 14:42:45 GMT 20060.408173979260027") %>
   is_admin: false
   first_name: Jane