Change custom_data column into payload/blob/data

[MartinMikita]

Possible change name of column custom_data into payload, blob or data.

Input search.tsv doesn't matter in this case, while the names of columns are defined in conf/sphinx/sphinx.conf script, and processed in websearch.py script - returned as JSON.

P.S. note that column date_filter is calculated with gawk command while reading input source file, and it is also returned in JSON. Changing this column requires also change in websearch.py:253 - see location of string in this repo.