Check if replace_and_search is allowed

Uses an explicit check at the requested type of action rather than
handling the default via else. A filter is also added to this check
that allows replace_and_search to be disabled so that only replace
can be used.

This filter - emr_enable_replace_and_search - can be used elsewhere
to show or hide replace and search options.
Add an emr_display_replace_type_options filter

This filter will allow others to decide if options should be
available when uploading a new image rather than allowing the
default behavior to just happen.
Wrap replace_and_search option with emr_enable_replace_and_search

This filter works hand in hand with the filter found in upload.php
to restrict unauthorized use of the replace and search function
Add emr_before_replace_type_options action to popup output

An action here allows custom HTML to be displayed, or other actions
taken, while the popup form is being output. This can aid with
messaging toward specific audiences on a multisite network.
Merge pull request #5 from jeremyfelt/replace-only

[PR] Add filters and actions for customization of plugin options