addition of a few new concepts

[schumannj]

I was missing a few concepts for annotating some quantities and sections in NOMAD:

• sample | en | The material of interest in an investigation.
• mass | en | The weight of an object.
• reaction conditions | en | Collection of environmental variables of a reaction such as temperature, pressure, reagent concentrations and flow rate.
• mechanism | en | A detailed description of the process leading from the reactants to the products of a reaction, including a characterization as complete as possible of the composition, structure, energy and other properties of reaction intermediates, products and transition states.
• elementary reaction | en | A reaction for which no reaction intermediates have been detected or need to be postulated in order to describe the chemical reaction on a molecular scale. An elementary reaction is assumed to occur in a single step and to pass through a single transition state.
• person | en | A physical entity which is a human beeing.
• preparator | en | The person carrying out a synthesis preparation.
• experimenter | en | The person starting or carrying out a planned process.
• dispersion | en | The fraction of atoms of a material located at the surface of a particle.