Not quite. I think the creators of Sigil are contemplating having some kind of sentence case/title case option... Right now I think Calibre has the regex functions which could do it but I haven't practiced enough with it to feel competent. I use the following regex to get it
mostly done:
find: <p
class="first">([A-Z])([A-Z ]+)*
replace: <p class="first">\1\L\2\E
I put the class="first" to designate the first paragraph in a chapter...you'll have to adjust.
I roll through the ePub one at a time in case it tries to change proper names or 'I' to lower case.
Not completely automatic...but 130 chapters shouldn't take more than a few minutes.