Support for .Net 4.5

- IReadOnlyCollection/List does no more expose Contains/IndexOf.
- LegacySupport/IReadOnlyCollection/List.cs:
  - contain definition that match the ones of .Net 4.5.
  - are exclude from build when targeting .Net 3.5 or .Net 4.0
Upgraded Tests for 4.0/4.5 support.
Removed Action Sequence (and other Breaking Changes).
MultiTrait in CK.Core.

- Removed CK.MultiTrait projects.
Namespace fix.
2.8.3 alpha version
Merge branch 'support-NET45' into activity-logger-traits

Conflicts:
	CK.MultiTrait/CK.MultiTrait.csproj
	Tests/CK.MultiTrait.Tests/CK.MultiTrait.Tests.csproj
Group conclusion are now tagged with CKTraits.

- Group conclusions can be injected explicitly while closing a group (marshaling calls from a Client to another Logger is now logically consistent: log can be reproduced identically).
- Tags on conclusion can be used to handle duplicated generated conclusions.
- Removed Mux/Demux from ActivityLogger.

- Removed Adapter class (Util now carries the poor 3 methods it contained).
- Removed ISimpleErrorMessage/ErrorMessage.
ActivityLogger now supports tags.
Bridge works.

- Cross AppDomain has yet to be tested.
Fixed comments.
Added tests & bug fix.
Ordering Traits and Contexts.

- Contexts have a Name and an internal unique index.
- Contexts are ordered (Separator => Name => Unique index).
- Traits are now orderable cross-contexts.
- Guards for null and context mismatch when combining Traits.
ActivityLogger now supports LogTime (UTC)

- DefaultActivityLogger does no more use Create: a
ctor exists.
- Removed useless TargetedPatchingOptOut.
Logging errors protection added.

- Tests have yet to be written.
LoggerError event exposes the error(s)
Release Candidate

- New CriticalErrorCollector is used by ActivityLogger.
- Lots of (successful) tests have been done.
Merge branch 'activity-logger-traits' into develop
Release 2.8.4-develop
Removes useless explicit implementation.

- DefaultActivityLogger class was hiding its Tap, PathCatcher
and ErrorCounter.