accounting: make P&L compatible with "british" accounting style

This report has always been based on "french layout", where there is first
all expenses on one page and all incomes on next page.

In the "british layout", there is only one sheet, showing income -
expense on the same layout ( as we can see today on
 https://en.wikipedia.org/wiki/Income_statement#Sample_income_statement
)

The idea is that we can configure financial section either with two
hierarchies for expense and income to have the french layout, or put all
the "british layout" hierarchy in income and leave expense empty.

bt5/erp5_accounting/SkinTemplateItem/portal_skins/erp5_accounting/AccountModule_viewProfitAndLossReport.oot

@@ -27,6 +27,7 @@
   xmlns:metal='http://xml.zope.org/namespaces/metal'
   tal:attributes='dummy python:request.RESPONSE.setHeader("Content-Type", "text/html;; charset=utf-8")'
   tal:define='portal python: context.getPortalObject();
+              has_income_and_expense_category python: bool(portal.portal_categories.financial_section.expense.contentValues());
               money_quantity_style python:portal.portal_preferences.getPreferredMoneyQuantityStyle("");
               money_currency_do_grouping python:"1234" in money_quantity_style and "false" or "true";
               at_date request/at_date/latestTime;
@@ -167,7 +168,8 @@
   <office:body>
 
     <office:spreadsheet>
-      <table:table table:style-name='ta1' table:print='false' table:name='Expense' tal:attributes="table:name portal/portal_categories/financial_section/expense/getTranslatedTitle">
+      <table:table tal:condition="has_income_and_expense_category"
+                   table:style-name='ta1' table:print='false' table:name='Expense' tal:attributes="table:name portal/portal_categories/financial_section/expense/getTranslatedTitle">
         <office:forms form:apply-design-mode='false' form:automatic-focus='false'/>
         <table:table-column table:style-name='co1' table:default-cell-style-name='report-title'/>
         <table:table-column table:style-name='co2' table:default-cell-style-name='ce7'/>
@@ -539,6 +541,8 @@
                                 global level2_title python:'';
                                 global level1_title python:'';">
 
+        <tal:block tal:condition="not: has_income_and_expense_category" metal:use-macro="template/macros/report_header"/>
+
         <!-- Header {{{ -->
         <table:table-header-rows>
         <table:table-row table:style-name='ro3'>
@@ -814,8 +818,9 @@
         </table:table-row>
         <!-- }}} --> 
 
+
         <!-- NET LOSS {{{ -->
-        <table:table-row tal:condition="python: net_income &gt; 0 or net_income_previous_period &gt; 0">
+        <table:table-row tal:condition="python: has_income_and_expense_category and (net_income &gt; 0 or net_income_previous_period &gt; 0)">
           <table:table-cell table:style-name='report-stat-heading2'
                             office:value-type='string'
                             table:number-rows-spanned='1'