Disable thousands separator in csv_export

csv_export() function in various files in Modules/feed/engine were using
the php function number_format() with 2 parameters which meant the
default thousands separator (comma) was being used when data points were
greater than 999
CSV export - add some user configuration options

Add configuration of parameters for controlling some aspects of CSV data
export to default_settings.php.

1. number of decimal places
2. decimal place separator
3. field separator

Notes:
1. This updates/enhances the original changes I proposed to
number_format() in commit/pull request
3c5751a7e21fab8798d34a2591c949b87489bbcd
2. The thousands separator is no longer used.  It is effectively
specified as 'nothing'.  Previously it defaulted to ','.
Revert "CSV export - add some user configuration options"

This reverts commit afa9f19551156f42f6c4b147d860b764396fe5a7.
 CSV export - add some user configuration options

User euqip provided some helpful suggestions regarding my original
changes.  This commit incorporates some of these.

Add configuration of parameters for controlling some aspects of CSV data
export to default_settings.php.

1. number of decimal places
2. decimal place separator
3. field separator

Notes:
1. This updates/enhances the original changes I proposed to
number_format() in commit/pull request
3c5751a
2. The thousands separator is no longer used.  It is effectively
specified as 'nothing'.  Previously it defaulted to ','.
Merge pull request #255 from prfemlchem/master

Disable thousands separator in csv_export