doc: Add cookbook item on creating custom content blocks

(cherry picked from commit 696e4e429ec90cba664be4dfaa97668c6c96a0bf)
mod_import_csv: improved parsing of CSV files, now handles quoted fields and performs automatic translation from latin-1 to utf-8
(cherry picked from commit 94e0a591ccd6f09d2a18f759c1a4458dcf12fd79)
mod_import_csv: remove stray underscore character from module name...
(cherry picked from commit e22b8fac9f768d9113e0cc04dc90b965d2c9a2b1)
mod_import_csv: remove superfluous lager messages about escaped chars.
(cherry picked from commit b647a46f56e984c90421b91c90231e2e87ecb56a)