#14 Verify addition

[lawson23]

99% of the time I have a file I download and a website
provides the md5 string shown in plain text and not a
md5 file. It would be nice that in MD5summer I could
click verify and choose either a MD5 file (as it does
now) or paste my MD5 text string and verify it against
a certain file.

Currently I have to either create a MD5 file against
the file downloaded and then look at the key compared
to the website or I have to create a txt file as an MD5
paste the hash key and then click verify.

I believe this would be a great addition for everyone
using the application!