Don't gray out unmovable blocks in read-only mode [finishes #67888684]

Was:

![image](https://f.cloud.github.com/assets/206973/2467991/70fc355c-afcb-11e3-8f85-09c6ceafef41.png)

now:

![image](https://f.cloud.github.com/assets/206973/2467992/749c4c74-afcb-11e3-84d5-66e08292109b.png)