Whitespace: remove unnecessary code indentation
Config report filter: added handling for invalid values in cookie

In some cases, the cookie could contain values which are no longer
applicable as filter criteria, e.g.
  - a project id which has been deleted
  - a user id for whom there are no config options
  - a config id for which there are no config options

The code now correctly handles these, by making sure that either the
filter criteria is dynamically updated to a valid value (ALL_PROJECTS
for projects), or the filter's selection list effectively includes the
invalid value (user id, config id), so that the displayed filter
reflects the actual data listed in the Database Configuration table.

Fixes the bug reported by atrol in issue #14559's bugnote 34648
Config report: preset the edit form to the current filter

The 'Username', 'Project Name' and 'Configuration Option' fields in the
'Set Configuration Option' form are now preset to the corresponding
value from the filter or defaulting to ALL_USERS, ALL_PROJECTS and blank
respectively if the filter is not defined or set to '[any]'.

This allows easier definition of related config, e.g. for a given
project or user.
Config report filter: added buttons to clear and reset default filter

This provides the user with a single-click way to

 - reset the filter to default settings
   (i.e. ALL_USERS, ALL_PROJECTS, [any] config).
 - clear the filter to display all configs
   (i.e. [any] user, [any] project, [any] config)

Issue #14559
Fix performance issue on adm_config_report.php

In systems with large numbers of config items in mantis_config_table, the
Configuration Report page can take a very long time to load.

This behavior is due to each of the 'Delete' buttons being printed with
its own form, each one having a security token. The performance
bottleneck is actually the serialize/unserialize calls executed while
storing/retrieving the token from the PHP session.

To avoid this problem, the print_button() and form_security_field()
functions have been modified to accept a security token as an optional
parameter. This allows the calling page to generate a single token,
which is shared by all buttons.

Furthermore, print_button() also allows the security token parameter to
be 'OFF', which prevents the function from displaying a security field.
This is useful for buttons not resulting in modifications (i.e. not
requiring CSRF protection).

Fixes #13680