Do not use t() in block plugins anymore

First attempt.

I've used this bash command to check for remaining t() usage:

find core -name Block -print | xargs grep -r "[^a-z|^>]t("

I continued with the script above and made a conversion script for ALL plugins changing all t() to $this->t():

find core | grep -v Derivative | grep -v FieldType | grep -v BlockManager\.php | grep \/Plugin\/[^/]*\/.*\.php | xargs sed -Ei .bak 's_([^a-z|^>])t\(_\1$this->t(_g'
find core -name *.bak -exec rm {} \;

Notice that the script skips the Derivative and FieldType plugins, and BlockManager. They don't implement a t() method yet.

Resulting patch is attached.