[NuGet] Handle errors when packages.config file cannot be read.

Fix unhandled exception when updating packages when packages.config
is invalid.

Fix unhandled exceptions in Add Packages dialog when packages.config
is invalid.

Show error message in Add Packages dialog when the packages.config
file cannot be read.
[NuGet] Fix icon for Package Console pad not being displayed.
[Ide] Attach editor extensions one by one

This allows editor extensions to inspect the already-attached extensions.
[Xml] Only attach one XML editor extension to a document
[Ide] Allow generators to override build action for generated file
[Xml] Fix invalid error locations in parser
[Xml] Parent opening nodes correctly in parser

BXC17822 - Errors in XML completion
Revert "[Xml] Parent opening nodes correctly in parser"

This reverts commit 091c1474892be25009c0da07d0a9cc4fa8823407.
[Xml] Add unit test for parser's tree mode
[Ide] Fix error when opening reference

Fixes 17784 - XS throws exception on clicking "System.Web.Entity"
reference file, which is missing
Updated reference to md-addins
Bump fsharpbinding
Merge remote-tracking branch 'origin/master' into fsharp

Conflicts:
	version-checks
Merge remote-tracking branch 'origin/master' into retina

Conflicts:
	version-checks
Fixed 'Bug 18232 - Unclosed XML brackets in documentation comments
`/// <` affect syntax highlighting of non-commented lines'.
Updated reference to md-addins
[NuGet] Disable Update/Restore menu items when there are no packages.
Fix ParsedTemplate to enable camelCase attributes

As for now, directive.Attributes is filled with "attName.ToLower()".

"Extract" method works on unchanged values and TemplatingEngine asks
for camelCase.

VisualStudio disregards the casing of parameters, so we can compare with
lower case.

This can be verified by using "linePragmas" attribute.

According to mhutch suggestion, fixed to use
StringComparer.OrdinalIgnoreCase.
[Ide] Some minor tweaks in welcome page reusability.
Fixed 'Bug 18228 - Automatic indentation mode doesn't remove trailing
whitespace'.