convert func_distr_shape type from foreign key to integer choices
Merge branch 'vuln-default-shape' into vuln-db03

Conflicts:
	openquakeplatform/openquakeplatform/vulnerability/models.py
add constraints on minimum_im and maximum_im based on function type
add evaluation_of_im field to EmpiricalModelInfo class
add mean_var_coef and sd_var_coef fields to FuncDistrVulnCont class
extract MODEL_TYPES from AnalyticalModelInfo and renamed it as ANALYTICAL_MODEL_TYPES
add specific CC_AnalyticalModelInfo for CapacityCurve
change help_text related to GeneralInformation::structure_type
add constraint on GeneralInformation::type_of_assessment depending on GeneralInformation::category
typos fixed