[Table] Add inline editing for inputs

#### Bug, feature request, or proposal:

Feature request

#### What is the expected behavior?

Clicking on a text field should launch a simple edit dialog with an `md-input`. Hitting Enter would then close the dialog and save the input as the new value for the text field.

#### What is the use-case or motivation for changing an existing behavior?

This behavior is described in the Data Table section of the Material spec, found [here](https://material.io/guidelines/components/data-tables.html#data-tables-interaction), and would be useful to have as its own component.

#### Is there anything else we should know?

Accessibility is a real concern here, and there doesn't seem to be much discussion/affordance defined in the spec for possible solutions. The text field itself could be defined as a button with `aria-role="button"`, but that may be deceptive.

cc @andrewseguin @jelbourn

Beginne damit, die angeforderte Interaktion und die verlinkte Material-Spezifikation für Datentabellen zu prüfen. Kläre den Ansatz zur Barrierefreiheit, bevor du die relevanten Einstiegspunkte für Tabelle und Eingabe identifizierst; abgeschlossen ist die Aufgabe, wenn Textfelder einen Bearbeitungsdialog öffnen, Enter den neuen Wert speichert und ihn schließt und die Interaktion barrierefrei ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.