Add a <select /> to choose the degree of the polynomial

[gdetrez]

• Use bootstrap inline form to arrange the select and the button
• Add a "degree of polynomial" label
• pass the selected degree to the api
• available values are 1 to 5 but that's easy to change

[coveralls]

Coverage increased (+0.1%) to 36.183% when pulling 3d1502c1b3b3335c8782b27cb67230c777cdd307 on gdetrez:polynomial-degree into 98207ba80163acc47dddc9a46a0c3348d3c1e931 on Scan-o-Matic:master.

[coveralls]

Changes Unknown when pulling 88ea8cdf56746e580ef1588f7609d61b4c0c2202 on gdetrez:polynomial-degree into on Scan-o-Matic:master.