Schema-Fieldname containing special chars causes graphql to fail

## Gentics Mesh Version, operating system, or hardware.
- v0.9.27

## Problem
If a schema or microschema contains a character which is not alphanumeric (or '_') all queries to graphql fail. With the following exception
`````
15:03:53.951 [Dumbstruck Monferno] ERROR [vert.x-eventloop-thread-4] [FailureHandler.java:91] - Error for request in path: /api/v1/kofl/graphql/?null
15:03:53.952 [Dumbstruck Monferno] ERROR [vert.x-eventloop-thread-4] [FailureHandler.java:93] - Error:
graphql.AssertException: Name must be non-null, non-empty and match [_A-Za-z][_0-9A-Za-z]*
at graphql.Assert.assertValidName(Assert.java:35) ~[mesh-server-0.9.27.jar:na]
at graphql.schema.GraphQLFieldDefinition.(GraphQLFieldDefinition.java:35) ~[mesh-server-0.9.27.jar:na]
at graphql.schema.GraphQLFieldDefinition$Builder.build(GraphQLFieldDefinition.java:215) ~[mesh-server-0.9.27.jar:na]
at com.gentics.mesh.graphql.type.field.FieldDefinitionProvider.createStringDef(FieldDefinitionProvider.java:173) ~[mesh-server-0.9.27.jar:na]
at com.gentics.mesh.graphql.type.field.MicronodeFieldTypeProvider.generateMicroschemaFieldType(MicronodeFieldTypeProvider.java:86) ~[mesh-server-0.9.27.
jar:na]
at com.gentics.mesh.graphql.type.field.MicronodeFieldTypeProvider.createType(MicronodeFieldTypeProvider.java:49) ~[mesh-server-0.9.27.jar:na]
at com.gentics.mesh.graphql.type.QueryTypeProvider.getRootSchema(QueryTypeProvider.java:436) ~[mesh-server-0.9.27.jar:na]
at com.gentics.mesh.graphql.GraphQLHandler.handleQuery(GraphQLHandler.java:56) ~[mesh-server-0.9.27.jar:na]
at com.gentics.mesh.graphql.GraphQLEndpoint.lambda$registerEndPoints$0(GraphQLEndpoint.java:50) ~[mesh-server-0.9.27.jar:na]
at io.vertx.ext.web.impl.RouteImpl.handleContext(RouteImpl.java:217) [mesh-server-0.9.27.jar:na]
at io.v
`````
And the following http-response body
`````
{
"message" : "Name must be non-null, non-empty and match [_A-Za-z][_0-9A-Za-z]*"
}
`````

## Expected behaviour

It should not be possible to add schemas or microschemas containing fieldnames with special chars. Alternatively the error message returned to the user should be more descriptive (containing the schema and fieldname where the error occurs)

Start with the GraphQL stack trace and inspect FieldDefinitionProvider.java, MicronodeFieldTypeProvider.java, QueryTypeProvider.java, and GraphQLHandler.java to trace where schema field names are turned into GraphQL fields. Determine whether invalid names are rejected during schema or microschema creation, or whether the GraphQL error can identify the schema and field. Done means invalid names no longer make GraphQL queries fail silently and the reported behavior is covered by the relevant verification.

Written by the indexing model from the issue text.