Added ability to replace a job when scheduling through Quartz

We've been using Topshelf to host our quartz services and have recently been asked to make sure the services work in a load balanced environment.  To do this we are using the built in functionality within Quartz but whenever we schedule a job via Topshelf it tries to create a new job which fails on the second machine as it already exists in the quartz tables.  To resolve this issue I've added an optional replaceJob parameter which will force Quartz to override the job if it has already been created by another node.