Add support for InChI structure queries

This adds support for using InChIs to specify a molcule
for structure/sub-structure searching. Now, if the string
starts with 'InChI=' the identifier will be interpreted as
an InChI.

Change-Id: I966c47eaabdbca2112095fcc30130d8bed551708
Add placeholder text for structure queries

This adds placeholder text for structure queries which
gives information and examples to the user.

Change-Id: Ifce27f9d8f9ae942ca2fb0a65e527dab00e0cbf6
Merge topic 'improve-structure-query' into master

f96e092a Add placeholder text for structure queries
122e3059 Add support for InChI structure queries