Allow customisation of the signs

Too many plugins use the default priority of 10 so they race/chase.
Allow uses to configure the priorities and make sure that the defaults
are documented.

support/custom_ui_vimrc

@@ -65,3 +65,10 @@ augroup TestUICustomistaion
   autocmd User VimspectorTerminalOpened call s:SetUpTerminal()
   autocmd User VimspectorUICreated call s:CustomiseWinBar()
 augroup END
+
+let g:vimspector_sign_priority = {
+  \    'vimspectorBP':         3,
+  \    'vimspectorBPCond':     2,
+  \    'vimspectorBPDisabled': 1,
+  \    'vimspectorPC':         999,
+  \ }