fixed bug with multiple choise problems, added select buttons for problems and sections
added statistics in xlsx
added statistics downloading for sections
added requirement of openpyxl
modified select lists, table\'s title, file name of statistics files
fixed bug, that if student doesnt answer a question, he wont be shown in the table of statistics for the question
fixed problem with sorting problems
addition for previous commit
added coloring of cells in tables depending of correctness, added dividing cells if problem include severeal subproblems
added coloring of cells in XLSX depending of answer' correctness, added dividing cells if problem include severeal subproblems
addition for previous commit
bug fix in html
Merge pull request #62 from pelikanchik/timur

Timur