Improve my.cnf to be Phabricator compliant

Improve the MySQL configuration to be compliant with Phabricator setup checks.

The change appends the following block to the [mysqld] section of the [mysqld] my.cnf:

# 
# * Phabricator specific settings
#
sql_mode=STRICT_ALL_TABLES
ft_stopword_file=/opt/phabricator/resources/sql/stopwords.txt   
ft_min_word_len=3
innodb_buffer_pool_size=410M