Enter key should perform search in search dialog

[Sa'ar Zac Elias]

Since there is no 'OK' button in the search and replace dialog, the enter key is useless. therefore, when in search tab, the enter key should trigger the search, and in replace dialog it should trigger the replace.

[Jakub Ś]

After consulting the problem with @Saare we agreed that CKEditor should follow MS notepad behavior.

When focus is in the input field, pressing ENTER should fire the search, in both dialogs.