Change "m_DefaultParam" tag to allow parameters with variable names/values

In-Portal has m_DefailtParam tag, which can be used to set template-wide default parameter values (in case if whoever includes that template don't pass any of parameters). Usually this is done like so:

<inp2:m_DefaultParam param1="value1" param2="value2"/>

If there is a need to set different default value based on other parameter value it's done like so:

<inp2:m_SetParam param3="value3"/>
<inp2:m_DefaultParam par{$param3}am1="value1" param2="val{$param3}ue2"/>

Actually there is no limit on where to inject other parameter value. However this construct doesn't work because of an error in current implementation of m_DefaultParam tag.