Fix increment and decrement usage with schemata

When working with Postgres and schemas lately, I noticed that increment/decrement operations did not work if I tried to specify a schema on my models. Other operations (select, delete, save, etc.) worked though, so we narrowed it down into 2 locations.

It looks like `.addSchema()` wasn't updated to only take in a single parameter (`this.Model`) and `.incrementQuery()` was incorrectly quoting the table name (which would work unless using a schema).

Code to duplicate (fails on current master, works with the PR):

```javascript
var Sequelize = require('sequelize')
  , sequelize = new Sequelize('test', 'postgres', '', {
      logging: false,
      dialect: 'postgres'
    })
  , myModel;

sequelize.dropSchema('mySchema')
  .then(function createSchema() {
    return sequelize.createSchema('myschema');
  })
  .then(function createModel() {

    myModel = sequelize.define('myModel', {
      id: {
        type: Sequelize.INTEGER,
        primaryKey: true
      },
      incremental: {
        type: Sequelize.INTEGER,
        defaultValue: 0
      }
    }, {
      schema: 'myschema'
    });

    return sequelize.sync();
  })
  .then(function createInstance() {
    return myModel.create({ id: 1, incremental: 2 });
  })
  .then(function incrementResult(instance) {
    return instance.increment('incremental', { by: 1 });
  })
  .then(function nope(result) {
    console.log('Increment worked!', result);
  })
  .catch(function failure(err) {
    console.log('Increment failed', err);
  });
```