declare AllowUnsafeBlocks=true in .csproj file or avoid unsafe code completly in project

[emanuelb]

Need to add:

<AllowUnsafeBlocks>true</AllowUnsafeBlocks>

in this <PropertyGroup> tag:

atomex.mobile/atomex/atomex.csproj

Lines 3 to 6 in 905735a

	<PropertyGroup>
	<TargetFramework>netstandard2.0</TargetFramework>
	<ProduceReferenceAssembly>true</ProduceReferenceAssembly>
	</PropertyGroup>

Otherwise compilation fail with errors such as:

Common/SecureStringExtensions.cs(66,17): error CS0227: Unsafe code may only appear if compiling with /unsafe [/home/appuser/app/atomex/atomex.mobile/atomex.client.core/Atomex.Client.Core/Atomex.Client.Core.csproj]

Adding /p:AllowUnsafeBlocks=true to msbuild is another solution but it's better to declare it in csproj file.