Filter muted submissions when suggesting work

Adds a unmuted_for(username) class method to submission with test and
chains that method in user to prevent muted suggestions from being mixed
in when random submissions are suggested. Fixes #747
Add empty test case to phone-number_test.hs

When solving the Haskell phone number assignment with a pattern match, one could get into a situation where the patterns are non-exhaustive for empty strings. The resulting error should be triggered by the automatic test. This commit adds another test case to assert that an empty string is treated like an invalid phone number.
Add test case with only invalid chars to phone-number_test.hs 

When solving the Haskell phone number assignment with a pattern match, one could get into a situation where the patterns are non-exhaustive for empty strings resulting from filtering all invalid characters. The resulting error should be triggered by the automatic test. This commit adds another test case to assert that a non-empty string with symbols and no digits is treated like an invalid phone number.
Fix tab highlighting issue for the tabs on the exercise pages, #759
haskell say
haskell secret-handshake
haskell series
haskell sieve
haskell simple-cipher
haskell strain
haskell sum-of-multiples
Remove outdated Lineman route stubs.

These were originaly in place to devlop the notification piece and the
api as since drifted. Removing them so using the lineman server piece no
longer breaks notifications.
Merge pull request #761 from etrepum/haskell-exercises

haskell say
Merge pull request #752 from bxt/patch-1

Add empty string test case to phone-number_test.hs
Merge pull request #760 from thewatts/master

Fix tab highlighting issue for the tabs on the exercise pages, #759
haskell nit fix, replace `intercalate " "` with `unwords`
Merge pull request #762 from etrepum/haskell-intercalate-to-unwords

haskell nit fix, replace `intercalate " "` with `unwords`
Revert "Fix tab highlighting issue for the tabs on the exercise pages, #759"

This reverts commit 5f0e6f47bc4590ea24ecd24e59e4a472576dad6b.
Fix bug in db:seed
Improve seed comment API