Add ignore to umbraco folder as it will be added by Install-Package UmbracoCms or updated by Update-Package UmbracoCms

In Umbraco v8 we have a new packages folder located under Umbraco/views/packages/...

This gets ignored by the current version. Adding this new line prevents this and includes all files and subfolders under this new location.

Considering the VisualStudio gitignore file contains a line "**/[Pp]ackages/*", these 2 lines from Umbraco gitignore never get applied properly to the desired files, even though Umbraco lines were added after the VS lines. I guess the VS's line is more specific, so it gets a priority of some sort.

The out of date models flag is automatically generated by the system, we don't want this in Git

Add ImageProcessor cached files and nuget package updates

This reverts commit 5b168d4300.

Amends #1131 - fixes Umbraco template to compensate for the change in the
VisualStudio template which would lead to issues if the two were used together.
These rules were originally added by @bbodenmiller in #1013

From the discussion on #1013:

Since the rule in VS is packages/*, the fact that it contains a slash means
that it is anchored to the top level. That is, is will only apply to
a directory called packages at the top level, and not to any at deeper
directories like App_Data. So these rules at the bottom of your changes
actually aren't necessary after all. I just confirmed this with a quick test.