Template processor setValue() improvements

[dmitryfar]

Template processor improvements:

in setValueForPart() method this strings manipulation calls for each document header, footer and main part:

    if (substr($search, 0, 2) !== '${' && substr($search, -1) !== '}') {
        $search = '${' . $search . '}';
    }

    if (!String::isUTF8($replace)) {
        $replace = utf8_encode($replace);
    }

Move it to setValue() method to reduce time of these operations.

Merged. Thank you, guys.