Allowing <usg> element in the <def> element

[daliboris]

In the Old Czech Dictionary and the Electronic Dictionary of Old Czech, the definition (in contemporary Czech) may contain word that "deviates in a certain respect from the main bulk of" the definition, for example (I'm not sure if the symptom translation is correct in English):

<def>přičesávat (<usg type="socioCultural">expr.</usg>), přikrášlovat, nepatřičně vylepšovat</def>

i.e.

<def>glitz up (<usg type="socioCultural">expr.</usg>), beautify, embellish, unduly improve</def>

<def>dostat se, dorazit, přibýt (<usg type="meaningType">kniž.</usg>)</def>

come, arrive, land (<usg type="meaningType">lit.</usg>)

Can we also use the <usg> tag in these cases?

[ttasovac]

Ongoing challenge. See #152