Better binary handling: Choose Strict or Legacy JSON serializer and inspect binary data in document viewer

Dear Mister Girbal,

thanks for your wonderful, easy to use and powerful efficient UMongo app.

We're using MongoDB a lot to store documents containing meta data (using strings, numbers and co) together with small binary data (files ~ 2 kbytes, mostly text files, but with unkown encoding, iso8859-1, utf8, utf16 ...).

To improve inspecting our collections, I have enhanced your super pratical and efficent UMongo viewer with two binary related improvements:
* Improved Binary Handling in Document Tree by adding several tree representations
* Allow to choose the JSON serializer mode Legacy or Strict when exporting documents to files.

Because this small improvements maybe helpful for others too, I invite you to have a look at the changes.
Maybe you find it useful and want them to merge and include in upcoming versions of UMongo.
I would absolutly understand if this is not the correct time to include them or if the cannot be applied because of other currently followed objectives or any other reason.

Yours sincerely,
Steffen Gürtler