Ensure definitions respect 'noImplicitAny'

[tbouffard]

Some elements defined in the lib version 1.0.2 currently do not respect that When use in a project with tsconfig noImplicitAny set to true, this generates some TypeScript errors like

• node_modules/mxgraph-type-definitions/handler/mxKeyHandler.d.ts(14,31): error TS7006: Parameter 'target' implicitly has an 'any' type
• node_modules/mxgraph-type-definitions/shape/mxStencil.d.ts(140,3): error TS7010: 'drawChildren', which lacks return-type annotation, implicitly has an 'any' return type.

Workaround: set skipLibCheck to true

[tbouffard]

@hungtcs I am working on this one, PR to come soon