Faster dotnet restore for backend container (#333)

* Faster `dotnet restore` for backend container

Now it will copy all the .csproj files into place before running `dotnet
restore` on any of them, which means the LexBoxApi.csproj file will be
able to find its dependent projects at restore time, and restore all of
them together.

* Address review comments

backend/LexBoxApi/dev.Dockerfile

@@ -9,7 +9,7 @@ WORKDIR /src/backend
 # Copy the main source project files
 COPY */*.csproj *.sln ./
 # move them into the proper sub folders, based on the name of the project
-RUN for file in $(ls *.csproj); do dir=${file%.*} mkdir -p ${file%.*}/ && mv $file ${file%.*}/ && dotnet restore ${file%.*}/${file}; done
+RUN for file in $(ls *.csproj); do dir=${file%.*} mkdir -p ${file%.*}/ && mv $file ${file%.*}/; done; dotnet restore FixFwData/FixFwData.csproj; dotnet restore LexBoxApi/LexBoxApi.csproj
 
 COPY . .
 WORKDIR /src/backend/LexBoxApi