Input component updates

[valentijnnieman]

edit:
This PR is becoming much bigger than expected, apologies in advance if the commit history or comments are not super clear.

This updates the Input component with a new debounce prop that determines when setProps is called, should fix #169. It also adds a bunch of unit tests, and fixes an issue where props coming from dash-renderer would overwrite the current state of the input. That last bug is more common than we think - components that use state as well as setProps get out of sync often.

Here's an example app with the new debounce prop:

import dash
from dash.dependencies import Input, Output
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash()
app.scripts.config.serve_locally = True

app.layout = html.Div([
    dcc.Input(placeholder='Enter a value...',
        type='number',
        value=0,
        step=0.01,
        debounce=True,
        id='input_id',
        style={'float': 'left'}),
    html.Div(id='my-div')
])

@app.callback(
    Output(component_id='my-div', component_property='children'),
    [Input(component_id='input_id', component_property='value')]
)
def update_output_div(input_value):
    return 'You\'ve entered (+1) {}'.format(input_value+1)

if __name__ == '__main__':
    app.run_server()

It also fixes #292 by fixing the step prop and #173 by not updating value if < min or > max.

Also renamed a couple of props that weren't being picked up by React, similarly to #348.