Wholesale cleanup of all history plugins

- remove the use of redundant cite
- minor cleanups to history.plugin.bash
- set explicit load orders for history-search and history-substring-search
- add new plugin history-eternal
- replace superfluous trap for managing HISTTIMEFORMAT changes

plugins/available/history-substring-search.plugin.bash

@@ -1,7 +1,9 @@
 # shellcheck shell=bash
-cite about-plugin
 about-plugin 'search history using the substring already entered'
 
+# Load after the history plugin
+# BASH_IT_LOAD_PRIORITY: 375
+
 # enter a few characters and press UpArrow/DownArrow
 # to search backwards/forwards through the history
 if [[ ${SHELLOPTS} =~ (vi|emacs) ]]; then