Add specs; minor changes to some commands

`:tabedit` now works as an alias to `:edit` with a path and
  as an alias to `:tabnew` without.
`:tabnew` is a new command that opens a new tab with a new file if used
 without a path and works as an alias to `:tabedit` with one.
`:tabclose` now works as a proper alias to `:quit` (i.e. passes the arguments)
`:edit` now works more like before - it opens a given path in a new tab.
 It also doesn't do anything if the file was modified since the last commit,
 unless forced by using `:edit!`
`:write` works properly again and doesn't overwrite files, unless forced by
 using `:write!`
`:xit` is now called `:xit` and not just `:x`
`:substitute` now properly replaces multiple groups (`:s/(a)b(c)/X\1\2X\0`)

lib/ex-command-mode-input-element.coffee

@@ -1,64 +0,0 @@
-class ExCommandModeInputElement extends HTMLDivElement
-  createdCallback: ->
-    @className = "command-mode-input"
-
-    @editorContainer = document.createElement("div")
-    @editorContainer.className = "editor-container"
-
-    @appendChild(@editorContainer)
-
-  initialize: (@viewModel, opts = {}) ->
-    if opts.class?
-      @editorContainer.classList.add(opts.class)
-
-    if opts.hidden
-      @editorContainer.style.height = "0px"
-
-    @editorElement = document.createElement "atom-text-editor"
-    @editorElement.classList.add('editor')
-    @editorElement.getModel().setMini(true)
-    @editorElement.setAttribute('mini', '')
-    @editorContainer.appendChild(@editorElement)
-
-    @singleChar = opts.singleChar
-    @defaultText = opts.defaultText ? ''
-
-    @panel = atom.workspace.addBottomPanel(item: this, priority: 100)
-
-    @focus()
-    @handleEvents()
-
-    this
-
-  handleEvents: ->
-    if @singleChar?
-      @editorElement.getModel().getBuffer().onDidChange (e) =>
-        @confirm() if e.newText
-    else
-      atom.commands.add(@editorElement, 'editor:newline', @confirm.bind(this))
-
-    atom.commands.add(@editorElement, 'core:confirm', @confirm.bind(this))
-    atom.commands.add(@editorElement, 'core:cancel', @cancel.bind(this))
-    atom.commands.add(@editorElement, 'blur', @cancel.bind(this))
-
-  confirm: ->
-    @value = @editorElement.getModel().getText() or @defaultText
-    @viewModel.confirm(this)
-    @removePanel()
-
-  focus: ->
-    @editorElement.focus()
-
-  cancel: (e) ->
-    @viewModel.cancel(this)
-    @removePanel()
-
-  removePanel: ->
-    atom.workspace.getActivePane().activate()
-    @panel.destroy()
-
-module.exports =
-document.registerElement("ex-command-mode-input"
-  extends: "div",
-  prototype: ExCommandModeInputElement.prototype
-)