[Workbench] Add Rename Context Action

[WrapEarnPass]

About this:
Workbench has a Sidebar context menu that includes create and delete, but no update features.
Add Rename to context menu.
Add icons and update terms to make it clear that Delete is DELETE, and Remove is "Remove from this Workbench"

[WrapEarnPass]

I checked out geany@98bcbee3b99d71dfcdd9d3556ace9530ceda818d
and rebuilt:
build@debian:~/Projects/geany-plugins-remote/geany-plugins$git log | head
commit bde2212

No make errors

$ make all
Making all in src
make[1]: Entering directory '/home/build/Projects/geany-plugins-remote/geany-plugins/workbench/src'
  CC       workbench_la-plugin_main.lo
  CC       workbench_la-workbench.lo
  CC       workbench_la-wb_globals.lo
  CC       workbench_la-wb_project.lo
  CC       workbench_la-dialogs.lo
  CC       workbench_la-wb_monitor.lo
  CC       workbench_la-search_projects.lo
  CC       workbench_la-menu.lo
  CC       workbench_la-popup_menu.lo
  CC       workbench_la-sidebar.lo
  CC       workbench_la-utils.lo
  CC       workbench_la-idle_queue.lo
  CC       workbench_la-tm_control.lo
  CCLD     workbench.la
make[1]: Leaving directory '/home/build/Projects/geany-plugins-remote/geany-plugins/workbench/src'
make[1]: Entering directory '/home/build/Projects/geany-plugins-remote/geany-plugins/workbench'
make[1]: Nothing to be done for 'all-am'.
make[1]: Leaving directory '/home/build/Projects/geany-plugins-remote/geany-plugins/workbench'

File creation, rename, deletion success. Workbench dirtree autorefreshed after every step to display the changes.

Directory creation, rename, deletion success as well, but that action doesnt create status messages.

FILE_CREATED: "/home/build/Projects/geany-plugins-remote/testdir"
Workbench-Message: 09:39:09.912: wb_monitor_file_changed_cb: event: 1
Workbench-Message: 09:39:16.506: wb_monitor_file_changed_cb: event: 2
Workbench-Message: 09:39:16.506: wb_monitor_file_changed_cb: Prj: "geany-plugins-remote" Dir: ".." FILE_DELETED: "/home/build/Projects/geany-plugins-remote/testdir"
Workbench-Message: 09:39:16.506: wb_monitor_file_changed_cb: event: 3
Workbench-Message: 09:39:16.506: wb_monitor_file_changed_cb: Prj: "geany-plugins-remote" Dir: ".." FILE_CREATED: "/home/build/Projects/geany-plugins-remote/renamedir"
Workbench-Message: 09:39:16.506: wb_monitor_file_changed_cb: event: 1
Workbench-Message: 09:39:21.686: wb_monitor_file_changed_cb: event: 2
Workbench-Message: 09:39:21.686: wb_monitor_file_changed_cb: Prj: "geany-plugins-remote" Dir: ".." FILE_DELETED: "/home/build/Projects/geany-plugins-remote/renamedir"

The only critical in geany --verbose is
(geany:115024): Workbench-CRITICAL **: 09:38:26.990: plugin_workbench_on_doc_close: assertion 'doc != NULL && doc->file_name != NULL' failed
This appears unrelated to the change.

[WrapEarnPass]

Moved this so I could change the Pull request to About this:
Standardize context naming based on Projorg
Add a rename context
Prettify menu labels
Fix a few compiler warnings
Was tested locally against 2.0 (Debian), but compile checked against master (upstream). There may be a upstream build problem due to that.

Closes #1565
Contributed under GNU GENERAL PUBLIC LICENSE Version 2