Improve error messages for dependency groups

[Vilmir]

Description

Given a paket.dependencies with a default Main group
And some other groups
When the user tries to update/remove a package ID not in the Main group
And he forgets to specify the group
Then the error message does only tell him that the package ID does not exist in group Main

Repro steps

Using a paket.dependencies with packages in default group and at least 1 dependency group named InternalTools with 1 package called A. The package A is only used in the dependency group, and not in default one

1. Call paket update nuget A
2. The error message only tells that package A does not exist in group Main

Expected behavior

PS C:\svn\ProjectSecret\trunk> ..paket\paket.exe update nuget A
Paket version 3.4.0.0
Paket failed with:
      Package A was not found in paket.dependencies in group Main.
      However, Package A was found in groups:
        - InternalTools
      You can use the command "group" to specify the dependency group of your package

Actual behavior

PS C:\svn\ProjectSecret\trunk> ..paket\paket.exe update nuget A
Paket version 3.4.0.0
Paket failed with:
      Package A was not found in paket.dependencies in group Main.

Known workarounds

Today, the developer needs to find the right group main himself.
He has to open the paket.dependencies file, search for his package ID and get the group name

[Vilmir]

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