Correspond to user's middle name

[kyoshizaki]

• Create middle_name and phonetic_middle_name columns for User tables.
• Make it possible to change the availability of middle name by the config file

[kyoshizaki]

won't fix this issue

There are countries where person names are separated by 4 parts.
Considering such a situation, it is difficult to store the each part of the names for all countries simply by adding a middle name column.

So for convenience, store the name as two parts (family_name and given_name) in the database.
And when letting the user input his / her name from the form, the contents of "name" to be input to the two parts can be indicated by the label tag.