GenericRepository Query functions. Improved error handling. Minor refactoring.
Using ValueOrError instead of exceptions in DSL parser for easier debugging and Debug-mode performace. ValueOrError was already partially implemented in the parser.
New concept: RowPermissions-AllowRead,
a helper for building the row permissions filter that allows combining multiple rules and inheriting rules from one entity to another.
Minor refactoring.
Cleaner reference path validation in Browse-Take concept.
New concept: RowPermissions-DenyRead.
Merge pull request #30 from sstublic/master

RowPermissionsWrite
Merge branch 'master' of https://github.com/Rhetos/Rhetos

Conflicts:
	CommonConcepts/Plugins/Rhetos.Dsl.DefaultConcepts/Rhetos.Dsl.DefaultConcepts.csproj
Fixing row permissions rules after merge.
Minor refactoring.
Refactoring server command utilities out of GenericRepository.