Remove the single breaking filter_input[INPUT_SERVER]

Fixes #254
Merge pull request #263 from x-team/issue-254

Remove the single breaking filter_input[INPUT_SERVER]
Basic class to replace filter_input functionality #257
Introduce xt_filter_var, switch instances of filter_var to it
Remove couple of not-needed filter_var instances
Differentiate between validation/sanitization filters
Add arguments to both functions to eliminate confusion
Add default value for `super` variable
Caught a filter_var trying to escape his destiny
Reuse WP_Stream_Settings::get_active_connectors()
Include connector class checking

Before adding & registering a connector, check if the connector's class
is a subclass of WP_Stream_Connector
Introduce WP_Stream_Connectors::admin_notices()

The new method is added to the admin_notices hook by load() and will
print messages stored in $admin_notices
Fix connector labels storing
Apply filters to stream query SQL
Revert "Apply filters to stream query SQL"

This reverts commit 062c6bff8daa9a3071b2e94085e8631f2a30adfd.
[issue-266] Apply filters to $sql
[issue-266] Document `wp_stream_query` filter
Minor improvement to docblock
Merge pull request #268 from x-team/issue-266

Issue 266: Allow stream query to be filterable
Change class/functions prefix from xt_ to wp_stream_
Merge branch 'develop' into issue-257

Conflicts:
	includes/log.php
Code formatting
Merge pull request #264 from x-team/issue-257

257: Basic class to replace filter_input functionality